LINER LTC1992-10HMS8 Low power, fully differential input/output amplifier/driver family Datasheet

LTC1992 Family
Low Power, Fully Differential
Input/Output
Amplifier/Driver Family
U
FEATURES
DESCRIPTIO
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The LTC®1992 product family consists of five fully differential, low power amplifiers. The LTC1992 is an unconstrained fully differential amplifier. The LTC1992-1,
LTC1992-2, LTC1992-5 and LTC1992-10 are fixed gain
blocks (with gains of 1, 2, 5 and 10 respectively) featuring
precision on-chip resistors for accurate and ultrastable
gain. All of the LTC1992 parts have a separate internal
common mode feedback path for outstanding output
phase balancing and reduced second order harmonics.
The VOCM pin sets the output common mode level independent of the input common mode level. This feature
makes level shifting of signals easy.
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■
■
■
■
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■
Adjustable Gain and Fixed Gain Blocks of 1, 2, 5
and 10
±0.3% (Max) Gain Error from –40°C to 85°C
3.5ppm/°C Gain Temperature Coefficient
5ppm Gain Long Term Stability
Fully Differential Input and Output
CLOAD Stable up to 10,000pF
Adjustable Output Common Mode Voltage
Rail-to-Rail Output Swing
Low Supply Current: 1mA (Max)
High Output Current: 10mA (Min)
Specified on a Single 2.7V to ±5V Supply
DC Offset Voltage <2.5mV (Max)
Available in 8-Lead MSOP Package
The amplifiers’ differential inputs operate with signals
ranging from rail-to-rail with a common mode level from
the negative supply up to 1.3V from the positive supply.
The differential input DC offset is typically 250µV. The railto-rail outputs sink and source 10mA. The LTC1992 is
stable for all capacitive loads up to 10,000pF.
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APPLICATIO S
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Differential Driver/Receiver
Differential Amplification
Single-Ended to Differential Conversion
Level Shifting
Trimmed Phase Response for Multichannel Systems
The LTC1992 can be used in single supply applications
with supply voltages as low as 2.7V. It can also be used
with dual supplies up to ±5V. The LTC1992 is available in
an 8-pin MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
Single-Supply, Single-Ended to Differential Conversion
10k
5V
5V
5V
3
10k
VIN
0V
–5V
1
7
2
10k
0.01µF
INPUT SIGNAL
FROM A
±5V SYSTEM
8
– +
VMID
VOCM
4
5V
2.5V
0V
LTC1992
+ –
5
6
5V
2.5V
0V
OUTPUT SIGNAL
FROM A
SINGLE-SUPPLY SYSTEM
10k
VIN
(5V/DIV)
0V
–5V
5V
+OUT
(2V/DIV)
–OUT
0V
1992 TA01b
1992 TA01a
1992f
1
LTC1992 Family
U
W W
W
ABSOLUTE
AXI U
RATI GS
(Note 1)
Total Supply Voltage (+V S to –V S) .......................... 12V
Maximum Voltage
on any Pin .......... (–VS – 0.3V) ≤ VPIN ≤ (+VS + 0.3V)
Output Short-Circuit Duration (Note 3) ............ Indefinite
Operating Temperature Range (Note 5)
LTC1992CMS8/LTC1992-XCMS8/
LTC1992IMS8/LTC1992-XIMS8 ..........–40°C to 85°C
LTC1992HMS8/LTC1992-XHMS8 .....–40°C to 125°C
Specified Temperature Range (Note 6)
LTC1992CMS8/LTC1992-XCMS8/
LTC1992IMS8/LTC1992-XIMS8 ..........–40°C to 85°C
LTC1992HMS8/LTC1992-XHMS8 .....–40°C to 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
U
U
W
PACKAGE/ORDER I FOR ATIO
TOP VIEW
–IN 1
VOCM 2
+VS 3
+OUT 4
+
–
+–
TOP VIEW
8
7
6
5
+IN
VMID
–VS
–OUT
–IN 1
VOCM 2
+VS 3
+OUT 4
+
–
+–
8
7
6
5
+IN
VMID
–VS
–OUT
MS8 PACKAGE
8-LEAD PLASTIC MSOP
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 250°C/W
TJMAX = 150°C, θJA = 250°C/W
ORDER PART
NUMBER
MS8 PART
MARKING
ORDER PART
NUMBER
MS8 PART
MARKING
LTC1992CMS8
LTC1992IMS8
LTC1992HMS8
LTYU
LTZC
LTAGR
LTC1992-1CMS8
LTC1992-1IMS8
LTC1992-1HMS8
LTC1992-2CMS8
LTC1992-2IMS8
LTC1992-2HMS8
LTC1992-5CMS8
LTC1992-5IMS8
LTC1992-5HMS8
LTC1992-10CMS8
LTC1992-10IMS8
LTC1992-10HMS8
LTACJ
LTACM
LTAFZ
LTYV
LTZD
LTAGA
LTACK
LTACN
LTAJH
LTACL
LTACP
LTAJJ
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1992f
2
LTC1992 Family
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to all parts in the LTC1992 family.
SYMBOL
PARAMETER
VS
Supply Voltage Range
IS
Supply Current
CONDITIONS
●
ALL C AND I GRADE
MIN
TYP
MAX
ALL H GRADE
MIN
TYP
MAX
2.7
2.7
VS = 2.7V to 5V
11
UNITS
11
V
●
0.65
0.75
0.7
0.8
1.0
1.2
1.2
1.5
0.65
0.8
0.7
0.9
1.0
1.5
1.2
1.8
mA
mA
mA
mA
±2.5
±2.5
±2.5
±0.25
±0.25
±0.25
±4
±4
±4
mV
mV
mV
●
VS = ±5V
VOSDIFF
Differential Offset Voltage
(Input Referred) (Note 7)
VS = 2.7V
VS = 5V
VS = ±5V
●
●
●
±0.25
±0.25
±0.25
∆VOSDIFF/∆T
Differential Offset Voltage Drift
(Input Referred) (Note 7)
VS = 2.7V
VS = 5V
VS = ±5V
●
●
●
10
10
10
PSRR
Power Supply Rejection Ratio
(Input Referred) (Note 7)
VS = 2.7V to ±5V
●
GCM
Common Mode Gain(VOUTCM/VOCM)
Common Mode Gain Error
Output Balance (∆VOUTCM/(∆VOUTDIFF) VOUTDIFF = –2V to +2V
Common Mode Offset Voltage
VS = 2.7V
VS = 5V
(VOUTCM – VOCM)
VS = ±5V
●
●
●
1
± 0.1
–85
±0.3
–60
1
±0.1
–85
±0.35
–60
%
dB
●
●
●
±0.5
±1
±2
±12
±15
±18
±0.5
±1
±2
±15
±17
±20
mV
mV
mV
∆VOSCM /∆T
Common Mode Offset Voltage Drift
●
●
●
10
10
10
VOUTCMR
Output Signal Common Mode Range
(Voltage Range for the VOCM Pin)
RINVOCM
Input Resistance, VOCM Pin
IBVOCM
Input Bias Current, VOCM Pin
VMID
Voltage at the VMID Pin
VOUT
Output Voltage, High
(Note 2)
VOSCM
VS = 2.7V
VS = 5V
VS = ±5V
●
VS = 2.7V to ±5V
75
80
(–VS)+0.5V
72
10
10
10
µV/°C
µV/°C
µV/°C
80
dB
10
10
10
(+VS)–1.3V (–VS)+0.5V
µV/°C
µV/°C
µV/°C
(+VS)–1.3V
V
●
500
500
MΩ
●
±2
±2
pA
●
2.44
2.50
VS = 2.7V, Load = 10k
VS = 2.7V, Load = 5mA
VS = 2.7V,Load = 10mA
●
●
●
2.60
2.50
2.29
2.69
2.61
2.52
Output Voltage, Low
(Note 2)
VS = 2.7V, Load = 10k
VS = 2.7V, Load = 5mA
VS = 2.7V, Load = 10mA
●
●
●
Output Voltage, High
(Note 2)
VS = 5V, Load = 10k
VS = 5V, Load = 5mA
VS = 5V, Load = 10mA
●
●
●
Output Voltage, Low
(Note 2)
VS = 5V, Load = 10k
VS = 5V, Load = 5mA
VS = 5V, Load = 10mA
●
●
●
Output Voltage, High
(Note 2)
VS = ±5V, Load = 10k
VS = ±5V, Load = 5mA
VS = ±5V, Load = 10mA
●
●
●
Output Voltage, Low
(Note 2)
VS = ±5V, Load = 10k
VS = ±5V, Load = 5mA
VS = ±5V, Load = 10mA
●
●
●
0.02
0.10
0.20
4.90
4.85
4.75
2.50
2.60
2.50
2.29
2.69
2.61
2.52
0.02
0.10
0.20
4.90
4.80
4.70
0.10
0.25
0.35
4.99
4.89
4.80
– 4.99
– 4.90
– 4.80
2.43
0.10
0.25
0.35
4.99
4.90
4.81
0.02
0.10
0.20
4.90
4.85
4.65
2.56
–4.90
–4.75
–4.65
0.10
0.25
0.41
V
V
V
V
V
V
0.10
0.30
0.42
4.99
4.89
4.80
–4.98
–4.90
–4.80
V
V
V
V
4.99
4.90
4.81
0.02
0.10
0.20
4.85
4.80
4.60
2.57
V
V
V
V
V
V
–4.85
–4.75
–4.55
V
V
V
1992f
3
LTC1992 Family
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to all parts in the LTC1992 family.
ALL C AND I GRADE
MIN
TYP
MAX
ALL H GRADE
MIN
TYP
MAX
SYMBOL
PARAMETER
CONDITIONS
ISC
Output Short-Circuit Current
Sourcing (Notes 2,3)
VS = 2.7V, VOUT = 1.35V
VS = 5V, VOUT = 2.5V
VS = ±5V, VOUT = 0V
●
●
●
20
20
20
30
30
30
20
20
20
30
30
30
mA
mA
mA
Output Short-Circuit Current Sinking
(Notes 2,3)
VS = 2.7V, VOUT =1.35V
VS = 5V, VOUT = 2.5V
VS = ±5V, VOUT = 0V
●
●
●
13
13
13
30
30
30
13
13
13
30
30
30
mA
mA
mA
80
dB
AVOL
●
Large-Signal Voltage Gain
80
UNITS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as
(+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Specifications applicable to the LTC1992 only.
LTC1992CMS8
LTC1992ISM8
MIN
TYP
MAX
LTC1992HMS8
MIN
TYP
MAX
2
250
2
400
100
0.1
150
SYMBOL
PARAMETER
CONDITIONS
IB
Input Bias Current
VS = 2.7V to ±5V
●
IOS
Input Offset Current
VS = 2.7V to ±5V
●
0.1
RIN
Input Resistance
●
500
500
MΩ
CIN
Input Capacitance
●
3
3
pF
en
Input Referred Noise Voltage Density f = 1kHz
35
35
nV/√Hz
in
Input Noise Current Density
1
1
fA/√Hz
VINCMR
Input Signal Common Mode Range
CMRR
Common Mode Rejection Ratio
(Input Referred)
SR
Slew Rate (Note 4)
GBW
Gain-Bandwidth Product
(fTEST = 100kHz)
f = 1kHz
●
VINCM = –0.1V to 3.7V
TA = 25°C
LTC1992CMS8
LTC1992IMS8/
LTC1992HMS8
(–VS)– 0.1V (+VS)– 1.3V (–VS)– 0.1V (+VS)– 1.3V
UNITS
pA
pA
V
●
69
90
69
90
dB
●
0.5
1.5
0.5
1.5
V/µs
3.0
3.2
3.5
3.0
3.2
2.5
1.9
3.0
4.0
4.0
1.9
●
●
3.5
4.0
MHz
MHz
MHz
1992f
4
LTC1992 Family
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the
LTC1992-1 only.
SYMBOL
PARAMETER
GDIFF
Differential Gain
Differential Gain Error
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
CONDITIONS
LTC1992-1CMS8
LTC1992-1IMS8
MIN
TYP
MAX
LTC1992-1HMS8
MIN
TYP
MAX
UNITS
1
±0.1
50
3.5
1
±0.1
50
3.5
V/V
%
ppm
ppm/°C
●
●
en
Input Referred Noise Voltage Density (Note 7) f = 1kHz
RIN
Input Resistance, Single-Ended +IN, –IN Pins
VINCMR
Input Signal Common Mode Range
VS = 5V
CMRR
Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
VINCM = –0.1V to 3.7V ●
55
60
SR
Slew Rate (Note 4)
●
0.5
1.5
GBW
Gain-Bandwidth Product
±0.3
45
●
22.5
30
45
37.5
22
– 0.1V to 4.9V
fTEST = 180kHz
±0.35
nV/√Hz
30
38
kΩ
– 0.1V to 4.9V
V
55
60
dB
0.5
1.5
V/µs
3
MHz
3
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as
(+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Typical values are at TA = 25°C. Specifications apply to the LTC1992-2 only.
SYMBOL
PARAMETER
GDIFF
Differential Gain
Differential Gain Error
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
CONDITIONS
LTC1992-2CMS8
LTC1992-2IMS8
MIN
TYP
MAX
LTC1992-2HMS8
MIN
TYP
MAX
UNITS
2
±0.1
50
3.5
2
±0.1
50
3.5
V/V
%
ppm
ppm/°C
●
●
en
Input Referred Noise Voltage Density (Note 7) f = 1kHz
RIN
Input Resistance, Single-Ended +IN, –IN Pins
VINCMR
Input Signal Common Mode Range
VS = 5V
CMRR
Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
VINCM = –0.1V to 3.7V ●
55
60
SR
Slew Rate (Note 4)
●
0.7
2
GBW
Gain-Bandwidth Product
45
●
fTEST = 180kHz
±0.3
22.5
30
45
37.5
22
– 0.1V to 4.9V
4
±0.35
30
nV/√Hz
38
kΩ
– 0.1V to 4.9V
V
55
60
dB
0.7
2
V/µs
4
MHz
1992f
5
LTC1992 Family
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the
LTC1992-5 only.
SYMBOL
PARAMETER
GDIFF
Differential Gain
Differential Gain Error
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
CONDITIONS
LTC1992-5CMS8
LTC1992-5IMS8
MIN
TYP
MAX
LTC1992-5HMS8
MIN
TYP
MAX
UNITS
5
±0.1
50
3.5
5
±0.1
50
3.5
V/V
%
ppm
ppm/°C
●
●
en
Input Referred Noise Voltage Density (Note 7) f = 1kHz
RIN
Input Resistance, Single-Ended +IN, –IN Pins
VINCMR
Input Signal Common Mode Range
VS = 5V
CMRR
Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
VINCM = –0.1V to 3.7V ●
55
60
SR
Slew Rate (Note 4)
●
0.7
2
GBW
Gain-Bandwidth Product
±0.3
45
●
22.5
30
45
37.5
22
– 0.1V to 3.9V
fTEST = 180kHz
±0.35
nV/√Hz
30
38
kΩ
– 0.1V to 3.9V
V
55
60
dB
0.7
2
V/µs
4
MHz
4
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as
(+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Typical values are at TA = 25°C. Specifications apply to the LTC1992-10 only.
SYMBOL
PARAMETER
GDIFF
Differential Gain
Differential Gain Error
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
CONDITIONS
LTC1992-10CMS8
LTC1992-10IMS8
MIN
TYP
MAX
LTC1992-10HMS8
MIN
TYP
MAX
UNITS
10
±0.1
50
3.5
10
±0.1
50
3.5
V/V
%
ppm
ppm/°C
●
●
en
Input Referred Noise Voltage Density (Note 7) f = 1kHz
RIN
Input Resistance, Single-Ended +IN, –IN Pins
VINCMR
Input Signal Common Mode Range
VS = 5V
CMRR
Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
VINCM = –0.1V to 3.7V ●
55
60
SR
Slew Rate (Note 4)
●
0.7
2
GBW
Gain-Bandwidth Product
45
●
fTEST = 180kHz
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Output load is connected to the midpoint of the +VS and –VS
potentials. Measurement is taken single-ended, one output loaded at a
time.
Note 3: A heat sink may be required to keep the junction temperature
below the absolute maximum when the output is shorted indefinitely.
Note 4: Differential output slew rate. Slew rate is measured single ended
and doubled to get the listed numbers.
Note 5: The LTC1992C/LTC1992-XC/LTC1992I/LTC1992-XI are guaranteed
functional over an operating temperature of –40°C to 85°C. The
LTC1992H/LTC1992-XH are guaranteed functional over the extended
operating temperature of – 40°C to 125°C.
±0.3
11.3
15
45
18.8
11
– 0.1V to 3.8V
4
±0.35
15
nV/√Hz
19
kΩ
– 0.1V to 3.8V
V
55
60
dB
0.7
2
V/µs
4
MHz
Note 6: The LTC1992C/LTC1992-XC are guaranteed to meet the specified
performance limits over the 0°C to 70°C temperature range and are
designed, characterized and expected to meet the specified performance
limits over the –40°C to 85°C temperature range but are not tested or QA
sampled at these temperatures. The LTC1992I/LTC1992-XI are guaranteed
to meet the specified performance limits over the –40°C to 85°C
temperature range. The LTC1992H/LTC1992-XH are guaranteed to meet
the specified performance limits over the –40°C to 125°C temperature
range.
Note 7: Differential offset voltage, differential offset voltage drift, CMRR,
noise voltage density and PSRR are referred to the internal amplifier’s
input to allow for direct comparison of gain blocks with discrete
amplifiers.
1992f
6
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Offset Voltage
vs Temperature (Note 7)
0.6
1.0
DIFFERENTIAL VOS (mV)
SUPPLY CURRENT (mA)
0.4
85°C
25°C
0.7
0.6
–40°C
0.5
0.4
0.3
0
VS = ±1.35V
VS = ±2.5V
–0.2
–0.4
VS = ±5V
–0.6
0.1
0
1
2 3 4 5 6 7 8
TOTAL SUPPLY VOLTAGE (V)
9
–0.8
–40
10
85
25
TEMPERATURE (°C)
–2
–3
25
85
TEMPERATURE (°C)
125
1992 G03
Common Mode Offset Voltage
vs VOCM Voltage
5
85°C
0
125°C
0
85°C
–10
–5
–40°C
–10
–15 +V = 5V
S
–VS = 0V
VINCM = 2.5V
–20
0 0.5 1 1.5 2 2.5 3 3.5
VOCM VOLTAGE (V)
–15 +V = 2.7V
S
–VS = 0V
VINCM = 1.35V
–20
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
VOCM VOLTAGE (V)
Output Voltage Swing
vs Output Load, VS = 2.7V
0.8
2.65
0.7
0.6
–40°C
–10
–15 +V = 5V
S
–VS = –5V
VINCM = 0V
–20
–5 –4 –3 –2 –1 0 1 2
VOCM VOLTAGE (V)
5
3
4
5
1992 G06
125°C
85°C
0.4
25°C
2.45
0.3
85°C
–40°C
125°C
2.35
2.30
0
5
–20 –15 –10 –5
10
LOAD CURRENT (mA)
15
20
1992 G07
1.0
4.95
0.9
4.90
0.8
4.80
4.65
0.2
25°C
4.75
4.70
0.7
125°C
–40°C
85°C
0.6
85°C
0.5
25°C
0.4
125°C
4.60
–SWING (V)
0.5
–SWING (V)
2.55
5.00
4.85
+SWING (V)
2.60
25°C
4.5
–5
Output Voltage Swing
vs Output Load, VS = 5V
2.70
–40°C
4
25°C
1992 G05
1992 G04
2.50
VOCM VOS (mV)
VOCM VOS (mV)
25°C
–40°C
+SWING (V)
VS = ±1.35V
–1
125°C
85°C
2.40
VS = ±2.5V
0
–5
–40
125
5
25°C
–5
1
Common Mode Offset Voltage
vs VOCM Voltage
125°C
0
VS = ±5V
2
1992 G02
Common Mode Offset Voltage
vs VOCM Voltage
5
VINCM = 0V
VOCM = 0V
–4
1992 G01
VOCM VOS (mV)
3
0.2
0.2
0
4
VINCM = 0V
VOCM = 0V
125°C
0.8
Common Mode Offset Voltage
vs Temperature
COMMON MODE VOS (mV)
Supply Current vs Supply Voltage
0.9
Applicable to all parts in the LTC1992 family.
0.3
–40°C
0.2
0.1
4.55
0.1
0
4.50
–20 –15 –10 –5 0
5 10
LOAD CURRENT (mA)
0
15
20
1992 G08
1992f
7
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to all parts in the LTC1992 family.
VOCM Input Bias Current
vs VOCM Voltage
Output Voltage Swing
vs Output Load, VS = ±5V
5.0
Differential Input Offset Voltage
vs Time (Normalized to t = 0)
10E-9
–3.8
100
TEMP = 35°C
–4.0
–40°C
–4.2
25°C
4.7
–4.4
125°C
85°C
85°C
4.6
125°C
–SWING (V)
+SWING (V)
4.8
–4.6
25°C
4.5
–4.8
–40°C
4.4
5
10
0
–20 –15 –10 –5
LOAD CURRENT (mA)
–5.0
15
125°C
1E-9
60
DELTA VOS (µV)
4.9
VOCM INPUT BIAS CURRENT (A)
80
100E-12
85°C
10E-12
–40°C
1E-12
0
20
0.5
1
–80
1.5 2 2.5 3 3.5
VOCM VOLTAGE (V)
4
4.5
–100
5
0
400
800
1200
TIME (HOURS)
1992 G10
Differential Gain vs Time
(Normalized to t = 0)
2000
Input Common Mode Overdrive
Recovery (Detailed View)
TEMP = 35°C
BOTH INPUTS
(INPUTS TIED TOGETHER)
BOTH INPUTS
(INPUTS TIED
TOGETHER)
6
1600
1992 G11
Input Common Mode Overdrive
Recovery (Expanded View)
8
4
0
1V/DIV
2
1V/DIV
DELTA GAIN (ppm)
0
–20
–60
1992 G09
10
20
–40
25°C
+VS = 5V
–VS = 0V
VINCM = 2.5V
100E-15
40
OUTPUTS
–2
–4
OUTPUTS
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
LTC1992-10 SHOWN
FOR REFERENCE
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
LTC1992-10 SHOWN
FOR REFERENCE
–6
–8
–10
0
400
800
1200
TIME (HOURS)
1600
2000
1992 G13
50µs/DIV
1µs/DIV
1992 G14
1992 G12
Output Overdrive Recovery
(Detailed View)
Output Overdrive Recovery
(Expanded View)
INPUTS
1V/DIV
1V/DIV
+VS = 2.5V, –VS = –2.5V, VOCM = 0V
OUTPUTS
OUTPUTS
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
LTC1992-2 SHOWN
FOR REFERENCE
LTC1992-2 SHOWN FOR REFERENCE
50µs/DIV
INPUTS
1992 G15
5µs/DIV
1992 G16
1992f
8
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
100
1000
FREQUENCY (kHz)
10000
12
6
0
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
10
– 20
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
–120
–140
–160
–180
100
1000
FREQUENCY (kHz)
10000
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
0.5
–40°C
125°C
85°C
–1.0
Differential Input Offset Voltage
vs Input Common Mode Voltage
2.0
1.0
0.5
–40°C
0
125°C
– 0.5
25°C
85°C
–1.0
1.0
0.5
–40°C
0
125°C
Common Mode Rejection Ratio
vs Frequency (Note 7)
–1.0
–2.0
–5 –4 –3 –2 –1 0 1 2 3
COMMON MODE VOLTAGE (V)
100
∆VS
∆VAMPDIFF
90
–VS
70
PSRR (dB)
+VS
60
50
40
30
20
20
∆VOUTCM
∆VOUTDIFF
–20
80
80
5
Output Balance vs Frequency
0
OUTPUT BALANCE (dB)
∆VAMPCM
∆VAMPDIFF
4
1922 G22
Power Supply Rejection Ratio
vs Frequency (Note 7)
40
85°C
1922 G21
1922 G20
60
25°C
–0.5
–1.5
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
+VS = 5V
–VS = –5V
VOCM = 0V
1.5
–2.0
–2.0
100
1000
1992 G37
–1.5
–1.5
120
100
FREQUENCY (kHz)
10
+VS = 5V
1.5 –VS = 0V
VOCM = 2.5V
1.0
0
CLOAD =
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
–100
2.0
+VS = 2.7V
–VS = 0V
1.5
VOCM = 1.35V
CMRR (dB)
– 80
Differential Input Offset Voltage
vs Input Common Mode Voltage
2.0
25°C
– 60
1992 G18
Differential Input Offset Voltage
vs Input Common Mode Voltage
–0.5
RIN = RFB = 10k
– 40
1992 G17
0
0
RIN = RFB = 10k
PHASE (DEG)
RIN = RFB = 10k
Differential Phase Response
vs Frequency
DIFFERENTIAL VOS (mV)
12
6
0
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
10
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
GAIN (dB)
GAIN (dB)
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Applicable to the LTC1992 only.
–40
–60
–80
10
0
100
0
1k
10k
100k
FREQUENCY (Hz)
1M
1992 G23
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G24
–100
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G25
1992f
9
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±1.5V
–VIN = 1.5V
CLOAD = 0pF
GAIN = 1
±
0V
VOUTDIFF (1V/DIV)
Differential Input Large-Signal
Step Response
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±1.5V
–VIN = 1.5V
GAIN = 1
±
VOUTDIFF (1V/DIV)
Differential Input Large-Signal
Step Response
Applicable to the LTC1992 only.
0V
CLOAD = 10000pF
CLOAD = 1000pF
2µs/DIV
20µs/DIV
1992 G26
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 4V
–VIN = 2V
CLOAD = 0pF
GAIN = 1
2.5V
Single-Ended Input Large-Signal
Step Response
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
Single-Ended Input Large-Signal
Step Response
1992 G27
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 4V
–VIN = 2V
GAIN = 1
2.5V
CLOAD = 10000pF
CLOAD = 1000pF
2µs/DIV
20µs/DIV
1992 G28
±
0V
VOUTDIFF (50mV/DIV)
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±50mV
–VIN = 50mV
CLOAD = 0pF
GAIN = 1
Differential Input Small-Signal
Step Response
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±50mV
–VIN = 50mV
GAIN = 1
±
VOUTDIFF (50mV/DIV)
Differential Input Small-Signal
Step Response
1992 G29
0V
CLOAD = 10000pF
CLOAD = 1000pF
1µs/DIV
1992 G30
10µs/DIV
1992 G31
1992f
10
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992 only.
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 200mV
–VIN = 100mV
CLOAD = 0pF
GAIN = 1
1µs/DIV
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 200mV
–VIN = 100mV
GAIN = 1
10µs/DIV
1992 G32
THD + Noise vs Frequency
THD + NOISE (dB)
–50
THD + Noise vs Amplitude
–40
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V
–60
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–50 –VS = –5V
VOCM = 0V
THD + NOISE (dB)
–40
VOUT = 10VP-PDIFF
VOUT = 5VP-PDIFF
–70
1992 G33
VOUT = 1VP-PDIFF
–80
–60
50kHz
20kHz
–70
10kHz
–80
5kHz
VOUT = 2VP-PDIFF
–90
–90
2kHz
–100
100
1k
10k
FREQUENCY (Hz)
50k
0.1
1
10
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
20
1992 G35
1992 G34
Differential Noise Voltage Density
vs Frequency
VOCM Gain vs Frequency,
VS = ±2.5V
5
1000
CLOAD = 10pF TO 10000pF
0
–5
GAIN (dB)
INPUT REFERRED NOISE (nV√Hz)
1kHz
–100
100
–10
–15
–20
–25
–30
–35
10
10
100
1000
FREQUENCY (Hz)
10000
1922 G36
10
100
1000
FREQUENCY (kHz)
10000
1992 G19
1992f
11
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
100
1000
FREQUENCY (kHz)
10000
12
6
0
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
10
0
–20
–40
PHASE (DEG)
12
6
0
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
10
Differential Phase Response
vs Frequency
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
GAIN (dB)
GAIN (dB)
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Applicable to the LTC1992-1 only.
–60
–80
CLOAD =
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
–100
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
–120
–140
–160
100
1000
FREQUENCY (kHz)
10000
–180
100
FREQUENCY (kHz)
10
1000
1992 G39
1992 G38
Differential Gain Error vs
Temperature
1992 G40
VOCM Gain vs Frequency
0.025
5
0.020
CLOAD = 10pF TO 10000pF
0
–5
0.010
0.005
GAIN (dB)
GAIN ERROR (%)
0.015
0
– 0.005
–10
–15
–20
– 0.010
–25
– 0.015
–30
– 0.020
– 0.025
–50
–35
–25
50
25
0
75
TEMPERATURE (°C)
100
125
100
1000
FREQUENCY (kHz)
10
1992 G42
1992 G41
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
1
–40°C
125°C
–1
25°C
–2
5
85°C
+VS = 5V
4 –VS = 0V
VOCM = 2.5V
3
4
2
1
0
–40°C
125°C
–1
–2
25°C
85°C
DIFFERENTIAL VOS (mV)
2
0
Differential Input Offset Voltage
vs Input Common Mode Voltage
5
+VS = 2.7V
4 –VS = 0V
VOCM = 1.35V
3
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
5
3
1
0
–1
–3
–4
–4
–4
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
1922 G43
–5
–5
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
1922 G44
125°C
–40°C
85°C
25°C
–2
–3
0
+VS = 5V
– VS = –5V
VOCM = 0V
2
–3
–5
10000
–5 –4 –3 –2 –1 0 1 2 3
COMMON MODE VOLTAGE (V)
4
5
1922 G45
1992f
12
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Common Mode Rejection Ratio
vs Frequency
100
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±1.5V
–VIN = 1.5V
90
80
70
CMRR (dB)
±
0V
VOUTDIFF (1V/DIV)
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±1.5V
–VIN = 1.5V
CLOAD = 0pF
Differential Input Large-Signal
Step Response
±
VOUTDIFF (1V/DIV)
Differential Input Large-Signal
Step Response
Applicable to the LTC1992-1 only.
0V
60
50
40
30
20
CLOAD = 10000pF
CLOAD = 1000pF
2µs/DIV
20µs/DIV
1992 G46
∆VAMPCM
∆VAMPDIFF
0
1k
100
10
1992 G47
10k
100k
FREQUENCY (Hz)
1M
1992 G48
2.5V
Power Supply Rejection Ratio
vs Frequency
100
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 4V
–VIN = 2V
90
80
70
PSRR (dB)
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 4V
–VIN = 2V
CLOAD = 0pF
Single-Ended Input Large-Signal
Step Response
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
Single-Ended Input Large-Signal
Step Response
2.5V
–VS
60
+VS
50
40
30
20
CLOAD = 10000pF
CLOAD = 1000pF
2µs/DIV
0
20µs/DIV
1992 G49
∆VS
∆VAMPDIFF
10
10
1992 G50
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G51
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±50mV
–VIN = 50mV
0V
–20
OUTPUT BALANCE (dB)
±
0V
Output Balance vs Frequency
0
VOUTDIFF (50mV/DIV)
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±50mV
–VIN = 50mV
CLOAD = 0pF
Differential Input Small-Signal
Step Response
±
VOUTDIFF (50mV/DIV)
Differential Input Small-Signal
Step Response
–40
–60
–80
CLOAD = 10000pF
CLOAD = 1000pF
1µs/DIV
1992 G52
10µs/DIV
∆VOUTCM
∆VOUTDIFF
–100
1992 G53
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G54
1992f
13
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Small-Signal
Step Response
Applicable to the LTC1992-1 only.
Differential Noise Voltage Density
vs Frequency
Single-Ended Input Small-Signal
Step Response
1000
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 200mV
–VIN = 100mV
CLOAD = 0pF
1µs/DIV
INPUT REFERRED NOISE (nV√Hz)
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 200mV
–VIN = 100mV
10
10µs/DIV
1992 G55
100
1992 G56
10
100
1000
FREQUENCY (Hz)
10000
1922 G57
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
–60
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–50 –VS = –5V
VOCM = 0V
THD + NOISE (dB)
THD + NOISE (dB)
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–50 –VS = –5V
VOCM = 0V
VOUT = 10VP-PDIFF
VOUT = 5VP-PDIFF
–70
VOUT = 1VP-PDIFF
–80
–60
50kHz
20kHz
–70
10kHz
–80
5kHz
VOUT = 2VP-PDIFF
–90
–90
2kHz
–100
100
1k
10k
FREQUENCY (Hz)
50k
1992 G58
1kHz
–100
0.1
1
10
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
20
1992 G59
1992f
14
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
18
12
6
0
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
10
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
100
1000
FREQUENCY (kHz)
10000
0
–20
–40
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
–60
–80
CLOAD =
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
–100
–120
–140
–160
100
1000
FREQUENCY (kHz)
10000
1992 G60
–180
10
100
FREQUENCY (kHz)
1000
1992 G61
Differential Gain Error vs
Temperature
1992 G62
VOCM Gain vs Frequency,
VS = ±2.5V
0.05
5
CLOAD = 10pF TO 10000pF
0.04
0
0.03
–5
0.02
0.01
GAIN (dB)
GAIN ERROR (%)
Differential Phase Response
vs Frequency
PHASE (DEG)
18
12
6
0
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
10
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
GAIN (dB)
GAIN (dB)
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Applicable to the LTC1992-2 only.
0
– 0.01
– 0.02
–10
–15
–20
– 0.03
–25
– 0.04
– 0.05
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
–30
125
10
100
1000
FREQUENCY (kHz)
1992 G64
1992 G63
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
2.0
25°C
–0.5
85°C
125°C
–1.0
1.0
–40°C
0.5
85°C
0
–0.5
25°C
125°C
–1.0
–1.5
–1.5
–2.0
+VS = 5V
1.5 –VS = –5V
VOCM = 0V
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
–40°C
0
2.0
+VS = 5V
1.5 –VS = 0V
VOCM = 2.5V
1.0
0.5
0
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
2.0
+VS = 2.7V
= 0V
1.5 –VS
VOCM = 1.35V
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
1992 G65
10000
1.0
–40°C
0.5
0
–0.5
85°C
25°C
125°C
–1.0
–1.5
–2.0
–2.0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
1992 G66
–5 –4 –3 –2 –1 0 1 2 3
COMMON MODE VOLTAGE (V)
4
5
1992 G67
1992f
15
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±750mV
–VIN = 750mV
CLOAD = 0pF
Differential Input Large-Signal
Step Response
100
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±750mV
–VIN = 750mV
±
90
80
70
CMRR (dB)
VOUTDIFF (1V/DIV)
0V
Common Mode Rejection Ratio
vs Frequency (Note 7)
±
VOUTDIFF (1V/DIV)
Differential Input Large-Signal
Step Response
Applicable to the LTC1992-2 only.
0V
60
50
40
30
20
CLOAD = 10000pF
CLOAD = 1000pF
2µs/DIV
1992 G68
∆VAMPCM
∆VAMPDIFF
10
20µs/DIV
0
100
1992 G69
1k
10k
100k
FREQUENCY (Hz)
1M
1992 G70
2.5V
Power Supply Rejection Ratio
vs Frequency (Note 7)
100
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 2V
–VIN = 1V
2.5V
90
–VS
80
+VS
70
PSRR (dB)
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 2V
–VIN = 1V
CLOAD = 0pF
Single-Ended Input Large-Signal
Step Response
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
Single-Ended Input Large-Signal
Step Response
60
50
40
30
20
CLOAD = 10000pF
CLOAD = 1000pF
2µs/DIV
0
20µs/DIV
1992 G71
∆VS
∆VAMPDIFF
10
1992 G72
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G73
Output Balance vs Frequency
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±25mV
–VIN = 25mV
0V
0
– 20
OUTPUT BALANCE (dB)
±
0V
VOUTDIFF (50mV/DIV)
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±25mV
–VIN = 25mV
CLOAD = 0pF
Differential Input Small-Signal
Step Response
±
VOUTDIFF (50mV/DIV)
Differential Input Small-Signal
Step Response
– 40
– 60
– 80
CLOAD = 10000pF
CLOAD = 1000pF
∆VOUTCM
∆VOUTDIFF
– 100
2µs/DIV
1992 G74
20µs/DIV
1992 G75
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G76
1992f
16
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Small-Signal
Step Response
Applicable to the LTC1992-2 only.
Differential Noise Voltage Density
vs Frequency
Single-Ended Input Small-Signal
Step Response
1000
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 100mV
–VIN = 50mV
CLOAD = 0pF
2µs/DIV
INPUT REFERRED NOISE (nV√Hz)
VOUTDIFF (50mV/DIV)
2.5V
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 100mV
–VIN = 50mV
100
10
20µs/DIV
1992 G77
1992 G78
10
100
1000
FREQUENCY (Hz)
10000
1922 G79
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–50 –VS = –5V
VOCM = 0V
50kHz
–50
–60
–70
THD + NOISE (dB)
THD + NOISE (dB)
VOUTDIFF (50mV/DIV)
CLOAD = 10000pF
CLOAD = 1000pF
VOUT = 1VP-PDIFF
VOUT = 2VP-PDIFF
–80
–90
–100
100
VOUT = 5VP-PDIFF
20kHz
–70
10kHz
5kHz
–80
2kHz
–90
VOUT = 10VP-PDIFF
1k
10k
FREQUENCY (Hz)
–60
1kHz
50k
1992 G80
–100
0.1
1
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
10
1992 G81
1992f
17
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
100
1000
FREQUENCY (kHz)
30
24
18
12
6
0
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
0
–20
–40
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
CLOAD =
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
–100
–160
–180
10000
100
FREQUENCY (kHz)
10
1992 G84
VOCM Gain vs Frequency
0.050
5
0.025
0
0
CLOAD = 10pF TO 10000pF
–5
GAIN (dB)
–0.025
–0.050
–0.075
–10
–15
–20
–0.100
–25
–0.125
–30
–25
50
25
0
75
TEMPERATURE (°C)
100
125
10
100
1000
FREQUENCY (kHz)
10000
1992 G86
1992 G85
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
0.5
–40°C
0
125°C
85°C
–1.0
1.0
0.5
–0.5
25°C
125°C
85°C
–1.0
–1.5
–2.0
–2.0
1922 G87
–40°C
0
–1.5
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
1.5
DIFFERENTIAL VOS (mV)
1.0
0
2.0
+VS = 5V
–VS = 0V
1.5
VOCM = 2.5V
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
+VS = 2.7V
–VS = 0V
1.5
VOCM = 1.35V
25°C
Differential Input Offset Voltage
vs Input Common Mode Voltage
2.0
2.0
–0.5
1000
1992 G83
Differential Gain Error vs
Temperature
GAIN ERROR (%)
–80
–140
1992 G82
–01.50
–50
–60
–120
100
1000
FREQUENCY (kHz)
10
10000
PHASE (DEG)
30
24
18
12
6
0
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
10
Differential Phase Response vs
Frequency
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
GAIN (dB)
GAIN (dB)
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Applicable to the LTC1992-5 only.
+VS = 5V
–VS = –5V
VOCM = 0V
1.0
0.5
0
–40°C
85°C
25°C
125°C
–0.5
–1.0
–1.5
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
1922 G88
–2.0
–5 –4 –3 –2 –1 0 1 2 3
COMMON MODE VOLTAGE (V)
4
5
1922 G89
1992f
18
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Common Mode Rejection Ratio
vs Frequency (Note 7)
100
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ± 300mV
–VIN = 300mV
90
80
70
CMRR (dB)
±
0V
VOUTDIFF (1V/DIV)
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ± 300mV
–VIN = 300mV
CLOAD = 0pF
Differential Input Large-Signal
Step Response
±
VOUTDIFF (1V/DIV)
Differential Input Large-Signal
Step Response
Applicable to the LTC1992-5 only.
0V
60
50
40
30
20
CLOAD = 10000pF
CLOAD = 1000pF
2µs/DIV
20µs/DIV
1992 G90
∆VAMPCM
∆VAMPDIFF
0
1k
100
10
1992 G91
10k
100k
FREQUENCY (Hz)
1M
1992 G92
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency (Note 7)
100
CLOAD = 10000pF
CLOAD = 1000pF
90
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 800mV
–VIN = 400mV
CLOAD = 0pF
2µs/DIV
70
PSRR (dB)
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
80
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 800mV
–VIN = 400mV
–VS
50
40
30
20
∆VS
∆VAMPDIFF
10
0
20µs/DIV
1992 G93
+VS
60
10
1992 G94
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G95
±
0V
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±10mV
–VIN = 10mV
0V
Output Balance vs Frequency
0
–20
OUTPUT BALANCE (dB)
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±10mV
–VIN = 10mV
CLOAD = 0pF
VOUTDIFF (50mV/DIV)
Differential Input Small-Signal
Step Response
±
VOUTDIFF (50mV/DIV)
Differential Input Small-Signal
Step Response
–40
–60
–80
∆VOUTCM
∆VOUTDIFF
CLOAD = 10000pF
CLOAD = 1000pF
–100
5µs/DIV
1992 G96
50µs/DIV
1992 G97
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G98
1992f
19
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-5 only.
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 40mV
–VIN = 20mV
CLOAD = 0pF
5µs/DIV
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 40mV
–VIN = 20mV
1992 G99
1000
INPUT REFERRED NOISE (nV√Hz)
Single-Ended Input Small-Signal
Step Response
100
10
50µs/DIV
1992 G100
10
100
1000
FREQUENCY (Hz)
10000
1922 G101
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
–60
–70
THD + NOISE (dB)
THD + NOISE (dB)
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–50 –VS = –5V
VOCM = 0V
VOUT = 1VP-PDIFF
VOUT = 2VP-PDIFF
VOUT = 5VP-PDIFF
–80
VOUT = 10VP-PDIFF
–90
–100
100
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–50 –VS = –5V
VOCM = 0V
50kHz
–60
20kHz
–70
10kHz
5kHz
2kHz
–80
–90
1k
10k
FREQUENCY (Hz)
50k
1992 G102
1kHz
–100
0.1
1
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
5
1992 G103
1992f
20
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
Differential Phase Response vs
Frequency
40
0
30
– 20
20
20
– 40
10
10
0
0
–10
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
–20
–30
–40
–50
–60
–10
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
–20
–30
–40
–50
–60
100
1000
FREQUENCY (kHz)
10
PHASE (DEG)
40
30
GAIN (dB)
GAIN (dB)
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Applicable to the LTC1992-10 only.
CLOAD =
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
–100
–140
–160
–180
100
FREQUENCY (kHz)
10
10000
1992 G105
1992 G104
Differential Gain Error vs
Temperature
1000
1992 G106
VOCM Gain vs Frequency
0.050
5
0.025
CLOAD = 10pF TO 10000pF
0
0
–0.025
–5
–0.050
GAIN (dB)
GAIN ERROR (%)
– 80
–120
100
1000
FREQUENCY (kHz)
10
10000
– 60
–0.075
–0.100
–0.125
–10
–15
–20
–0.150
–25
–0.175
–0.200
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
–30
125
100
1000
FREQUENCY (kHz)
10
1992 G107
Differential Input Offset Voltage
vs Input Common Mode Voltage
–40°C
125°C
–0.5
85°C
1.5
1.0
0.5
0
–0.5
–40°C
125°C
25°C
85°C
–1.0
–1.5
–1.5
0
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
1922 G109
+VS = 5V
– VS = –5V
VOCM = 0V
1.0
0.5
–40°C
0
–0.5
25°C
85°C
125°C
–1.0
–1.5
–2.0
–2.0
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
0.5
25°C
2.0
+VS = 5V
1.5 – VS = 0V
VOCM = 2.5V
1.0
–1.0
Differential Input Offset Voltage
vs Input Common Mode Voltage
2.0
+VS = 2.7V
– VS = 0V
1.5
VOCM = 1.35V
0
1992 G108
Differential Input Offset Voltage
vs Input Common Mode Voltage
2.0
10000
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
1922 G110
–2.0
–5 –4 –3 –2 –1 0 1 2 3
COMMON MODE VOLTAGE (V)
4
5
1922 G111
1992f
21
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Common Mode Rejection Ratio
vs Frequency (Note 7)
100
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±150mV
–VIN = 150mV
90
80
70
CMRR (dB)
±
0V
VOUTDIFF (1V/DIV)
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±150mV
–VIN = 150mV
CLOAD = 0pF
Differential Input Large-Signal
Step Response
±
VOUTDIFF (1V/DIV)
Differential Input Large-Signal
Step Response
Applicable to the LTC1992-10 only.
0V
60
50
40
30
20
CLOAD = 10000pF
CLOAD = 1000pF
2µs/DIV
20µs/DIV
1992 G112
∆VAMPCM
∆VAMPDIFF
10
0
100
1992 G113
1k
10k
100k
FREQUENCY (Hz)
1M
1992 G114
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency (Note 7)
100
CLOAD = 10000pF
CLOAD = 1000pF
90
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 400mV
–VIN = 200mV
CLOAD = 0pF
2µs/DIV
+VS
70
PSRR (dB)
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
80
2.5V
20µs/DIV
60
50
40
30
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 400mV
–VIN = 200mV
1992 G115
–VS
20
∆VS
∆VAMPDIFF
10
0
10
1992 G116
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G117
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response
Output Balance vs Frequency
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±5mV
–VIN = 5mV
0V
–20
OUTPUT BALANCE (dB)
±
0V
VOUTDIFF (50mV/DIV)
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±5mV
–VIN = 5mV
CLOAD = 0pF
±
VOUTDIFF (50mV/DIV)
0
–40
–60
–80
–100
CLOAD = 10000pF
CLOAD = 1000pF
10µs/DIV
1992 G118
100µs/DIV
∆VOUTCM
∆VOUTDIFF
–120
1992 G119
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
1992 G120
1992f
22
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Small-Signal
Step Response
Applicable to the LTC1992-10 only.
Differential Noise Voltage Density
vs Frequency
Single-Ended Input Small-Signal
Step Response
1000
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 20mV
–VIN = 10mV
CLOAD = 0pF
10µs/DIV
INPUT REFERRED NOISE (nV√Hz)
VOUTDIFF (50mV/DIV)
2.5V
2.5V
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 20mV
–VIN = 10mV
100µs/DIV
1992 G121
1992 G122
100
10
10
100
1000
FREQUENCY (Hz)
10000
1922 G123
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–50 –VS = –5V
VOCM = 0V
–60
–70
50kHz
–50
THD + NOISE (dB)
THD + NOISE (dB)
VOUTDIFF (50mV/DIV)
CLOAD = 10000pF
CLOAD = 1000pF
VOUT = 1VP-PDIFF
VOUT = 2VP-PDIFF
VOUT = 5VP-PDIFF
–80
10kHz
–70
5kHz
2kHz
–80
1kHz
–90
–100
100
20kHz
–60
–90
1k
10k
FREQUENCY (Hz)
50k
1992 G124
–100
0.1
1
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
2
1992 G125
1992f
23
LTC1992 Family
U
U
U
PI FU CTIO S
+VS, –VS (Pins 3, 6): The +VS and –VS power supply pins
should be bypassed with 0.1µF capacitors to an adequate
analog ground or ground plane. The bypass capacitors
should be located as closely as possible to the supply pins.
–IN, +IN (Pins 1, 8): Inverting and Noninverting Inputs of
the Amplifier. For the LTC1992 part, these pins are connected directly to the amplifier’s P-channel MOSFET input
devices. The fixed gain LTC1992-X parts have precision,
on-chip gain setting resistors. The input resistors are
nominally 30k for the LTC1992-1, LTC1992-2 and
LTC1992-5 parts. The input resistors are nominally 15k
for the LTC1992-10 part.
+OUT, –OUT (Pins 4, 5): The Positive and Negative
Outputs of the Amplifier. These rail-to-rail outputs are
designed to drive capacitive loads as high as 10,000pF.
VMID (Pin 7): Mid-Supply Reference. This pin is connected
to an on-chip resistive voltage divider to provide a midsupply reference. This provides a convenient way to set
the output common mode level at half-supply. If used for
this purpose, Pin 2 will be shorted to Pin 7, Pin 7 should
be bypassed with a 0.1µF capacitor to ground. If this
reference voltage is not used, leave the pin floating.
VOCM (Pin 2): Output Common Mode Voltage Set Pin. The
voltage on this pin sets the output signal’s common mode
voltage level. The output common mode level is set
independent of the input common mode level. This is a
high impedance input and must be connected to a known
and controlled voltage. It must never be left floating.
W
BLOCK DIAGRA S
(1992)
+VS
3
+VS
–IN 1
V+
+
200k –VS
+
4 +OUT
∑
30k
VMID 7
200k
–
V–
+
–
A1
A2
+
30k
VOCM 2
+
+VS
–
∑
5 –OUT
1992 BD
+IN 8
–VS
6
–VS
1992f
24
LTC1992 Family
W
BLOCK DIAGRA S
(1992-X)
+VS
3
+VS
–IN
RFB
RIN
1
200k
–VS
VMID
+VS
200k
RIN
+IN
+OUT
+ –
5
–OUT
RFB
8
RFB
30k 30k
30k 60k
30k 150k
15k 150k
–VS
6
–VS
W
RIN
4
2
VOCM
1992-X BD
U
PART
LTC1992-1
LTC1992-2
LTC1992-5
LTC1992-10
– +
7
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APPLICATIO S I FOR ATIO
Theory of Operation
The LTC1992 family consists of five fully differential, low
power amplifiers. The LTC1992 is an unconstrained fully
differential amplifier. The LTC1992-1, LTC1992-2,
LTC1992-5 and LTC1992-10 are fixed gain blocks (with
gains of 1, 2, 5 and 10 respectively) featuring precision onchip resistors for accurate and ultra stable gain.
In many ways, a fully differential amplifier functions much
like the familiar, ubiquitous op amp. However, there are
several key areas where the two differ. Referring to Figure 1, an op amp has a differential input, a high open-loop
gain and utilizes negative feedback (through resistors) to
set the closed-loop gain and thus control the amplifier’s
gain with great precision. A fully differential amplifier has
all of these features plus an additional input and a complementary output. The complementary output reacts to the
input signal in the same manner as the other output, but
in the opposite direction. Two outputs changing in an
equal but opposite manner require a common reference
point (i.e., opposite relative to what?). The additional
input, the VOCM pin, sets this reference point. The voltage
on the VOCM input directly sets the output signal’s com-
mon mode voltage and allows the output signal’s common
mode voltage to be set completely independent of the
input signal’s common mode voltage. Uncoupling the
input and output common mode voltages makes signal
level shifting easy.
For a better understanding of the operation of a fully differential amplifier, refer to Figure 2. Here, the LTC1992 functional block diagram adds external resistors to realize a basic
gain block. Note that the LTC1992 functional block diagram
is not an exact replica of the LTC1992 circuitry. However,
the Block Diagram is correct and is a very good tool for
understanding the operation of fully differential amplifier
circuits. Basic op amp fundamentals together with this block
diagram provide all of the tools needed for understanding
fully differential amplifier circuit applications.
The LTC1992 Block Diagram has two op amps, two
summing blocks (pay close attention the signs) and four
resistors. Two resistors, RMID1 and RMID2, connect directly to the VMID pin and simply provide a convenient
midsupply reference. Its use is optional and it is not
involved in the operation of the LTC1992’s amplifier. The
LTC1992 functions through the use of two servo networks
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Fully Differential Amplifier
Op Amp
–
–IN
–IN
LTC1992
AO
VOCM
OUT
+
+IN
+IN
• DIFFERENTIAL INPUT
• HIGH OPEN-LOOP GAIN
• SINGLE-ENDED OUTPUT
•
•
•
•
Op Amp with Negative Feedback
– +
+ –
RIN
Fully Differential Amplifier with Negative Feedback
RFB
RIN
–
–
–VIN
LTC1992
+
+VOUT
VOCM
–VOUT
VOCM
LTC1992
VOUT
RIN
+
–OUT
DIFFERENTIAL INPUT
HIGH OPEN-LOOP GAIN
DIFFERENTIAL OUTPUT
VOCM INPUT SETS OUTPUT
COMMON MODE LEVEL
RFB
VIN
+OUT
LTC1992
AO
–
+
+VIN
R
GAIN = – FB
RIN
VOCM
R
GAIN = – FB
RIN
RFB
1992 F01
Figure 1. Comparison of an Op Amp and a Fully Differential Amplifier
RFB
+VS
3
LTC1992
RIN
+VIN
–IN
1
INM
V+
+
RMID1
200k
SP
+
4
∑
V–
–
+
–
A1
A2
VOCM 2
+
RCMM
30k
+
–
RIN
–VIN
+IN
8
INP
+VOUT
RCMP
30k
VMID 7
RMID2
200k
+OUT
∑
5
–OUT
–VOUT
SM
6
–VS
RFB
1992 F02
Figure 2. LTC1992 Functional Block Diagram with External Gain Setting Resistors
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each employing negative feedback and using an op amp’s
differential input to create the servo’s summing junction.
One servo controls the signal gain path. The differential input
of op amp A1 creates the summing junction of this servo.
Any voltage present at the input of A1 is amplified (by the
op amp’s large open-loop gain), sent to the summing blocks
and then onto the outputs. Taking note of the signs on the
summing blocks, op amp A1’s output moves +OUT and
–OUT in opposite directions. Applying a voltage step at the
INM node increases the +OUT voltage while the –OUT voltage decreases. The RFB resistors connect the outputs to the
appropriate inputs establishing negative feedback and closing the servo’s loop. Any servo loop always attempts to drive
its error voltage to zero. In this servo, the error voltage is
the voltage between the INM and INP nodes, thus A1 will
force the voltages on the INP and INM nodes to be equal
(within the part’s DC offset, open loop gain and bandwidth
limits). The “virtual short” between the two inputs is conceptually the same as that for op amps and is critical to understanding fully differential amplifier applications.
The other servo controls the output common mode level.
The differential input of op amp A2 creates the summing
junction of this servo. Similar to the signal gain servo
above, any voltage present at the input of A2 is amplified,
sent to the summing blocks and then onto the outputs.
However, in this case, both outputs move in the same
direction. The resistors RCMP and RCMM connect the +OUT
and –OUT outputs to A2’s inverting input establishing
negative feedback and closing the servo’s loop. The midpoint of resistors RCMP and RCMM derives the output’s
common mode level (i.e., its average). This measure of the
output’s common mode level connects to A2’s inverting
input while A2’s noninverting input connects directly to
the VOCM pin. A2 forces the voltages on its inverting and
noninverting inputs to be equal. In other words, it forces
the output common mode voltage to be equal to the
voltage on the VOCM input pin.
For any fully differential amplifier application to function
properly both the signal gain servo and the common mode
level servo must be satisfied. When analyzing an applications circuit, the INP node voltage must equal the INM
node voltage and the output common mode voltage must
equal the VOCM voltage. If either of these servos is taken
out of the specified areas of operation (e.g., inputs taken
beyond the common mode range specifications, outputs
hitting the supply rails or input signals varying faster than
the part can track), the circuit will not function properly.
Fully Differential Amplifier Signal Conventions
Fully differential amplifiers have a multitude of signals and
signal ranges to consider. To maintain proper operation
with conventional op amps, the op amp’s inputs and its
output must not hit the supply rails and the input signal’s
common mode level must also be within the part’s specified limits. These considerations also apply to fully differential amplifiers, but here there is an additional output to
consider and common mode level shifting complicates
matters. Figure 3 provides a list of the many signals and
specifications as well as the naming convention. The
phrase “common mode” appears in many places and often
leads to confusion. The fully differential amplifier’s ability
to uncouple input and output common mode levels yields
great design flexibility, but also complicates matters some.
For simplicity, the equations in Figure 3 also assume an
ideal amplifier and perfect resistor matching. For a detailed analysis, consult the fully differential amplifier applications circuit analysis section..
Basic Applications Circuits
Most fully differential amplifier applications circuits employ symmetrical feedback networks and are familiar
territory for op amp users. Symmetrical feedback networks require that the –VIN/+VOUT network is a mirror
image duplicate of the +VIN/–VOUT network. Each of these
half circuits is basically just a standard inverting gain op
amp circuit. Figure 4 shows three basic inverting gain op
amp circuits and their corresponding fully differential
amplifier cousins. The vast majority of fully differential
amplifier circuits derive from old tried and true inverting
op amp circuits. To create a fully differential amplifier
circuit from an inverting op amp circuit, first simply
transfer the op amp’s VIN/VOUT network to the fully differential amplifier’s –VIN/+VOUT nodes. Then, take a mirror
image duplicate of the network and apply it to the fully
differential amplifier’s +VIN/–VOUT nodes. Op amp users
can comfortably transfer any inverting op amp circuit to a
fully differential amplifier in this manner.
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RFB
RIN
A
INM
2AVP-P –VIN
–A
VINDIFF
4AVP-PDIFF
RIN
2AVP-P +VIN
–A
+VOUT
VOCM LTC1992
VOCM
VINCM
A
– +
INP
B
–B
2BVP-P
VOUTDIFF
4BVP-PDIFF
VOUTCM
+ –
–VOUT
B
–B
2BVP-P
RFB
1992 F03
DIFFERENTIAL = V
INDIFF = +VIN – –VIN
INPUT VOLTAGE
DIFFERENTIAL
= VOUTDIFF = +VOUT – –VOUT
OUTPUT VOLTAGE
+VIN + –VIN
INPUT COMMON = V
INCM =
2
MODE VOLTAGE
+VOUT + –VOUT
OUTPUT COMMON = V
OUTCM =
2
MODE VOLTAGE
(
(
)
)
+VOUT = +VIN – –VIN •
1 RFB
•
+ VOCM
2 RIN
; VOSCM = 0V
–VOUT = –VIN – +VIN •
1 RFB
•
+ VOCM
2 RIN
; VOSCM = 0V
RFB
VOUTDIFF = VINDIFF • R
IN
VAMPDIFF = VINP – VINM
VAMPCM =
VINP + VINM
2
VOUTCM = VOCM
CMRR =
∆VAMPCM
; +VIN = –VIN
∆VAMPDIFF
∆VOUTCM
∆VOUTDIFF
OUTPUT BALANCE =
eNOUT =
( )√
RFB
+1 •
RIN
eNIN2 + rN2 WHERE: eNOUT = OUTPUT REFERRED NOISE VOLTAGE DENSITY
eNIN = INPUT REFERRED NOISE VOLTAGE DENSITY
(
)
RIN • RFB
rN ≈ (0.13nV/√Hz) R + R
IN
FB
(RESISTIVE NOISE IS ALREADY INCLUDED IN THE
SPECIFICATIONS FOR THE FIXED GAIN LTC1992-X PARTS)
VOSDIFFOUT = VOSDIFFIN •
( )
RFB
+1
RIN
VOSCM = VOUTCM – VOCM
Figure 3. Fully Differential Amplifier Signal Conventions (Ideal Amplifier and Perfect Resistor Matching is Assumed)
Single-Ended to Differential Conversion
One of the most important applications of fully differential amplifiers is single-ended signaling to differential
signaling conversion. Many systems have a single-ended
signal that must connect to an ADC with a differential
input. The ADC could be run in a single-ended manner,
but performance usually degrades. Fortunately, all of
basic applications circuits shown in Figure 4, as well as
all of the fixed gain LTC1992-X parts, are equally suitable
for both differential and single-ended input signals. For
single-ended input signals, connect one of the inputs to
a reference voltage (e.g., ground or midsupply) and
connect the other to the signal path. There are no tradeoffs
here as the part’s performance is the same with singleended or differential input signals. Which input is used
for the signal path only affects the polarity of the differential output signal.
Signal Level Shifting
Another important application of fully differential amplifier
is signal level shifting. Single-ended to differential conversion accompanied by a signal level shift is very commonplace when driving ADCs. As noted in the theory of
operation section, fully differential amplifiers have a common mode level servo that determines the output common
mode level independent of the input common mode level.
To set the output common mode level, simply apply the
desired voltage to the VOCM input pin. The voltage range on
the VOCM pin is from (–VS + 0.5V) to (+VS – 1.3V).
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Gain Block
RFB
RIN
RIN
–
VIN
RFB
VOUT
+
+ –
+VIN
R
GAIN = FB
RIN
CIN
AC Coupled Gain Block
–
RFB
RIN
VOUT
CIN
+ –
+VIN
RIN
–VOUT
RFB
Single Pole Lowpass Filter
C
RFB
RFB
RIN
–
VIN
+VOUT
VOCM LTC1992
RIN
S
H(S) = HO •
S + ωP
R
1
HO = FB ; ωP =
RIN
RIN • CIN
C
+
–
–VIN
+
–VOUT
RFB
CIN
RIN
VIN
+VOUT
VOCM LTC1992
RIN
RFB
+
–
–VIN
VOUT
+
+ –
+VIN
ωP
S + ωP
RFB
RFB
1
;ω =
RIN P RFB • C
C
H(S) = HO •
3-Pole Lowpass Filter
R2
+VOUT
VOCM LTC1992
RIN
WHERE HO =
+
–
–VIN
–VOUT
R2
C1
R1
R3
VIN
C1
–
R1
R3
R1
C2
2
R3
–VIN
R4
C2
VOUT
C3
+
+VIN
–
R4
+
+VOUT
C3
2
VOCM LTC1992
R4
+ –
–VOUT
C1
H(S) = HO
( )(
ωP
S + ωP
ωO2
ωO
2
S +S
+ ωO2
Q
)
R2
1992 F04
WHERE HO = R2 ; ωP = 1 ; ωO =
R4C3
R1
Q=
R1 • √R2R3
•
R1 R2 + R1 R2 + R2 R3
1
R2R3C1C2
C2
C1
Figure 4. Basic Fully Differential Amplifier Application Circuits (Note: Single-Ended to Differential Conversion is
Easily Accomplished by Connecting One of the Input Nodes, +VIN or –VIN, to a DC Reference Level (e.g.,
Ground))
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The VOCM input pin has a very high input impedance and
is easily driven by even the weakest of sources. Many
ADCs provide a voltage reference output that defines
either its common mode level or its full-scale level. Apply
the ADC’s reference potential either directly to the VOCM
pin or through a resistive voltage divider depending on the
reference voltage’s definition. When controlling the VOCM
pin by a high impedance source, connect a bypass capacitor (1000pF to 0.1µF) from the VOCM pin to ground to lower
the high frequency impedance and limit external noise
coupling. Other applications will want the output biased at
a midpoint of the power supplies for maximum output
voltage swing. For these applications, the LTC1992 provides a midsupply potential at the VMID pin. The VMID pin
connects to a simple resistive voltage divider with two
200k resistors connected between the supply pins. To use
this feature, connect the VMID pin to the VOCM pin and
bypass this node with a capacitor.
One undesired effect of utilizing the level shifting function
is an increase in the differential output offset voltage due
to gain setting resistor mismatch. The offset is approximately the amount of level shift (VOUTCM – VINCM) multiplied by the amount of resistor mismatch. For example, a
2V level shift with 0.1% resistors will give around 2mV of
output offset (2 • 0.1% = 2mV). The exact amount of offset
is dependent on the application’s gain and the resistor
mismatch. For a detail description, consult the Fully Differential Amplifier Applications Circuit Analysis section.
CMRR and Output Balance
dominates low frequency CMRR performance. The specifications for the fixed gain LTC1992-X parts include the
on-chip resistor matching effects. Also, note that an input
common mode signal appears as a differential output
signal reduced by the CMRR. As with op amps, at higher
frequencies the CMRR degrades. Refer to the Typical
Performance plots for the details of the CMRR performance over frequency.
At low frequencies, the output balance specification is
determined by the matching of the on-chip RCMM and
RCMP resistors. At higher frequencies, the output balance
degrades. Refer to the typical performance plots for the
details of the output balance performance over frequency.
Input Impedance
The input impedance for a fully differential amplifier application circuit is similar to that of a standard op amp
inverting amplifier. One major difference is that the input
impedance is different for differential input signals and
single-ended signals. Referring to Figure 3, for differential
input signals the input impedance is expressed by the
following expression:
RINDIFF = 2 • RIN
For single-ended signals, the input impedance is expressed by the following expression:
RINS-E =
RIN
RFB
1–
2 • (RIN + RFB )
One common misconception of fully differential amplifiers
is that the common mode level servo guarantees an
infinite common mode rejection ratio (CMRR). This is not
true. The common mode level servo does, however, force
the two outputs to be truly complementary (i.e., exactly
opposite or 180 degrees out of phase). Output balance is
a measure of how complementary the two outputs are.
The input impedance for single-ended signals is slightly
higher than the RIN value since some of the input signal is
fed back and appears as the amplifier’s input common
mode level. This small amount of positive feedback increases the input impedance.
At low frequencies, CMRR is primarily determined by the
matching of the gain setting resistors. Like any op amp,
the LTC1992 does not have infinite CMRR, however resistor mismatching of only 0.018%, halves the circuit’s
CMRR. Standard 1% tolerance resistors yield a CMRR of
about 40dB. For most applications, resistor matching
The LTC1992 family of parts is stable for all capacitive
loads up to at least 10,000pF. While stability is guaranteed,
the part’s performance is not unaffected by capacitive
loading. Large capacitive loads increase output step response ringing and settling time, decrease the bandwidth
Driving Capacitive Loads
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and increase the frequency response peaking. Refer to the
Typical Performance plots for small-signal step response,
large-signal step response and gain over frequency to
appraise the effects of capacitive loading. While the consequences are minor in most instances, consider these
effects when designing application circuits with large
capacitive loads.
Input Signal Amplitude Considerations
For application circuits to operate correctly, the amplifier
must be in its linear operating range. To be in the linear
operating range, the input signal’s common mode voltage
must be within the part’s specified limits and the rail-torail outputs must stay within the supply voltage rails.
Additionally, the fixed gain LTC1992-X parts have input
protection diodes that limit the input signal to be within the
supply voltage rails. The unconstrained LTC1992 uses
external resistors allowing the source signals to go beyond the supply voltage rails.
When taken outside of the linear operating range, the
circuit does not perform as expected, however nothing
extreme occurs. Outputs driven into the supply voltage
rails are simply clipped. There is no phase reversal or
oscillation. Once the outputs return to the linear operating
range, there is a small recovery time, then normal operation proceeds. When the input common mode voltage is
below the specified lower limit, on-chip protection diodes
conduct and clamp the signal. Once the signal returns to
the specified operating range, normal operation proceeds.
If the input common mode voltage goes slightly above the
specified upper limit (by no more than about 500mV), the
amplifier’s open-loop gain reduces and DC offset and
closed-loop gain errors increase. Return the input back to
the specified range and normal performance commences.
If taken well above the upper limit, the amplifier’s input
stage is cut off. The gain servo is now open loop; however,
the common mode servo is still functional. Output balance
is maintained and the outputs go to opposite supply rails.
However, which output goes to which supply rail is
random. Once the input returns to the specified input
common mode range, there is a small recovery time then
normal operation proceeds.
The LTC1992’s input signal common mode range (VINCMR)
is from (–VS – 0.1V) to (+VS – 1.3V). This specification
applies to the voltage at the amplifier’s input, the INP and
INM nodes of Figure 2. The specifications for the fixed gain
LTC1992-X parts reflect a higher maximum limit as this
specification is for the entire gain block and references the
signal at the input resistors. Differential input signals and
single-ended signals require a slightly different set of
formulae. Differential signals separate very nicely into
common mode and differential components while single
ended signals do not. Refer to Figure 5 for the formulae for
calculating the available signal range. Additionally, Table 1
lists some common configurations and their appropriate
signal levels.
The LTC1992’s outputs allow rail-to-rail signal swings.
The output voltage on either output is a function of the
input signal’s amplitude, the gain configured and the
output signal’s common mode level set by the VOCM pin.
For maximum signal swing, the VOCM pin is set at the
midpoint of the supply voltages. For other applications,
such as an ADC driver, the required level must fall within
the VOCM range of (–VS + 0.5V) to (+VS – 1.3V). For singleended input signals, it is not always obvious which output
will clip first thus both outputs are calculated and the
minimum value determines the signal limit. Refer to
Figure 5 for the formulae and Table 1 for examples.
To ensure proper linear operation both the input common
mode level and the output signal level must be within the
specified limits. These same criteria are also present with
standard op amps. However, with a fully differential amplifier, it is a bit more complex and old familiar op amp
intuition often leads to the wrong result. This is especially
true for single-ended to differential conversion with level
shifting. The required calculations are a bit tedious, but are
necessary to guarantee proper linear operation.
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Differential Input Signals
RFB
A
2AVP-P –VIN
–A
VINDIFF
4AVP-PDIFF
INM
RIN NODE
VOCM
VINCM
RIN
A
2AVP-P +VIN
–A
INP
NODE
– +
B
+VOUT
VOCM LTC1992
+ –
–B
2BVP-P
VOUTDIFF
4BVP-PDIFF
VOUTCM
–VOUT
B
–B
2BVP-P
R
G = FB
RIN
RFB
INPUT COMMON MODE LIMITS
A. CALCULATE VINCM MINIMUM AND MAXIMUM GIVEN RIN, RFB AND VOCM
1
VINCM(MAX) = (+VS – 1.3V) +
(+VS – 1.3V – VOCM)
G
1
VINCM(MIN) = (–VS – 0.1V) +
(–VS – 0.1V – VOCM)
G
OR B. WITH A KNOWN VINCM, RIN, RFB AND VOCM, CALCULATE COMMON MODE
VOLTAGE AT INP AND INM NODES (VINCM(AMP)) AND CHECK THAT IT IS
WITHIN THE SPECIFIED LIMITS.
V + VINM
1
G
=
V
+
V
VINCM(AMP) = INP
2
G + 1 INCM G + 1 OCM
OUTPUT SIGNAL CLIPPING LIMIT
VINDIFF(MAX)(VP-PDIFF) = THE LESSER VALUE OF
4
4
(+VS – VOCM) OR (VOCM – –VS)
G
G
Single End Input Signals
RFB
INM
RIN NODE
VINREF
VOCM
RIN
A
VREF
–A
2AVP-P
VINSIG
INP
NODE
– +
+VOUT
VOCM LTC1992
+ –
B
–B
2BVP-P
VOUTDIFF
4BVP-PDIFF
VOUTCM
–VOUT
B
–B
2BVP-P
R
G = FB
RIN
RFB
INPUT COMMON MODE LIMITS (NOTE: FOR THE FIXED GAIN LTC1992-X PARTS, VINREF AND VINSIG CANNOT EXCEED THE SUPPLIES)
VINSIG(MAX) = 2
VINSIG(MIN) = 2
OR
VINSIGP-P = 2
(
(
(
) (
) (
) (
V
1
+VS – 1.3V – VOCM
+VS – 1.3V – INREF +
2
G
V
1
–VS – 0.1V – INREF +
–VS – 0.1V – VOCM
2
G
(+VS – –VS) – 1.2V +
)
)
)
1
(+VS – –VS) – 1.2V
G
OUTPUT SIGNAL CLIPPING LIMIT
2
2
(+VS – VOCM) OR VINREF + (VOCM – –VS)
G
G
2
2
VINSIG(MIN) = THE GREATER VALUE OF VINREF + (–VS – VOCM) OR VINREF + (VOCM – +VS)
G
G
VINSIG(MAX) = THE LESSER VALUE OF VINREF +
1992 F05
Figure 5. Input Signal Limitations
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Table 1. Input Signal Limitations for Some Common Applications
Differential Input Signal, VOCM at Midsupply. (VINCM must be within the Min and Max table values and
VINDIFF must be less than the table value)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINCM(MAX)
(V)
VINCM(MIN)
(V)
VINDIFF(MAX)
(VP-PDIFF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7
0
1
1.35
1.450
–1.550
5.40
5.40
2.7
0
2
1.35
1.425
–0.825
2.70
5.40
2.7
0
5
1.35
1.410
–0.390
1.08
5.40
2.7
0
10
1.35
1.405
–0.245
0.54
5.40
5
0
1
2.5
4.900
–2.700
10.00
10.00
5
0
2
2.5
4.300
–1.400
5.00
10.00
5
0
5
2.5
3.940
–0.620
2.00
10.00
5
0
10
2.5
3.820
–0.360
1.00
10.00
5
–5
1
0
7.400
–10.200
20.00
20.00
5
–5
2
0
5.550
–7.650
10.00
20.00
5
–5
5
0
4.440
–6.120
4.00
20.00
5
–5
10
0
4.070
–5.610
2.00
20.00
Differential Input Signal, VOCM at Typical ADC Levels. (VINCM must be within the Min and Max table values and
VINDIFF must be less than the table value)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINCM(MAX)
(V)
VINCM(MIN)
(V)
VINDIFF(MAX)
(VP-PDIFF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7
0
1
1
1.800
–1.200
4.00
4.00
2.7
0
2
1
1.600
–0.650
2.00
4.00
2.7
0
5
1
1.480
–0.320
0.80
4.00
2.7
0
10
1
1.440
–0.210
0.40
4.00
5
0
1
2
5.400
–2.200
8.00
8.00
5
0
2
2
4.550
–1.150
4.00
8.00
5
0
5
2
4.040
–0.520
1.60
8.00
5
0
10
2
3.870
–0.310
0.80
8.00
5
–5
1
2
5.400
–12.200
12.00
12.00
5
–5
2
2
4.550
–8.650
6.00
12.00
5
–5
5
2
4.040
–6.520
2.40
12.00
5
–5
10
2
3.870
–5.810
1.20
12.00
1992f
33
LTC1992 Family
U
W
U U
APPLICATIO S I FOR ATIO
Table 1. Input Signal Limitations for Some Common Applications
Midsupply Referenced Single-Ended Input Signal, VOCM at Midsupply. (The VINSIG Min and Max values listed account for both the input
common mode limits and the output clipping)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINREF
(V)
VINSIG(MAX)
(V)
VINSIG(MIN)
(V)
VINSIGP-P(MAX)
(VP-P AROUND VINREF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7
0
1
1.35
1.35
1.550
–1.350
0.40
0.40
2.7
0
2
1.35
1.35
1.500
0.000
0.30
0.60
2.7
0
5
1.35
1.35
1.470
0.810
0.24
1.20
2.7
0
10
1.35
1.35
1.460
1.080
0.22
2.20
5
0
1
2.5
2.5
7.300
–2.500
9.60
9.60
5
0
2
2.5
2.5
5.000
0.000
5.00
10.00
5
0
5
2.5
2.5
3.500
1.500
2.00
10.00
5
0
10
2.5
2.5
3.000
2.000
1.00
10.00
5
–5
1
0
0
10.000
–10.000
20.00
20.00
5
–5
2
0
0
5.000
–5.000
10.00
20.00
5
–5
5
0
0
2.000
–2.000
4.00
20.00
5
–5
10
0
0
1.000
–1.000
2.00
20.00
Midsupply Referenced Single-Ended Input Signal, VOCM at Typical ADC Levels. (The VINSIG Min and Max values listed account for both
the input common mode limits and the output clipping)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINREF
(V)
VINSIG(MAX)
(V)
VINSIG(MIN)
(V)
VINSIGP-P(MAX)
(VP-P AROUND VINREF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7
0
1
1
1.35
2.250
–0.650
1.80
1.80
2.7
0
2
1
1.35
1.850
0.350
1.00
2.00
2.7
0
5
1
1.35
1.610
0.950
0.52
2.60
2.7
0
10
1
1.35
1.530
1.150
0.36
3.60
5
0
1
2
2.5
6.500
–1.500
8.00
8.00
5
0
2
2
2.5
4.500
0.500
4.00
8.00
5
0
5
2
2.5
3.300
1.700
1.60
8.00
5
0
10
2
2.5
2.900
2.100
0.80
8.00
5
–5
1
2
0
6.000
–6.000
12.00
12.00
5
–5
2
2
0
3.000
–3.000
6.00
12.00
5
–5
5
2
0
1.200
–1.200
2.40
12.00
5
–5
10
2
0
0.600
–0.600
1.20
12.00
1992f
34
LTC1992 Family
U
W
U U
APPLICATIO S I FOR ATIO
Table 1. Input Signal Limitations for Some Common Applications
Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Midsupply. (The VINSIG Min and Max values listed account for
both the input common mode limits and the output clipping)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINREF
(V)
VINSIG(MAX)
(V)
VINSIG(MIN)
(V)
VINSIGP-P(MAX)
(VP-P AROUND VINREF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7
0
1
1.35
0
2.700
–2.700
5.40
5.40
2.7
0
2
1.35
0
1.350
–1.350
2.70
5.40
2.7
0
5
1.35
0
0.540
–0.540
1.08
5.40
2.7
0
10
1.35
0
0.270
–0.270
0.54
5.40
5
0
1
2.5
0
5.000
–5.000
10.00
10.00
5
0
2
2.5
0
2.500
–2.500
5.00
10.00
5
0
5
2.5
0
1.000
–1.000
2.00
10.00
5
0
10
2.5
0
0.500
–0.500
1.00
10.00
Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Typical ADC Reference Levels. (The VINSIG Min and Max values
listed account for both the input common mode limits and the output clipping)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINREF
(V)
VINSIG(MAX)
(V)
VINSIG(MIN)
(V)
VINSIGP-P(MAX)
(VP-P AROUND VINREF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7
0
1
1
0
2.000
–2.000
4.00
4.00
2.7
0
2
1
0
1.000
–1.000
2.00
4.00
2.7
0
5
1
0
0.400
–0.400
0.80
4.00
2.7
0
10
1
0
0.200
–0.200
0.40
4.00
5
0
1
2
0
4.000
–4.000
8.00
8.00
5
0
2
2
0
2.000
–2.000
4.00
8.00
5
0
5
2
0
0.800
–0.800
1.60
8.00
5
0
10
2
0
0.400
–0.400
0.80
8.00
Fully Differential Amplifier Applications
Circuit Analysis
All of the previous applications circuit discussions have
assumed perfectly matched symmetrical feedback networks. To consider the effects of mismatched or asymmetrical feedback networks, the equations get a bit messier.
Figure 6 lists the basic gain equation for the differential
output voltage in terms of +VIN, –VIN, VOSDIFF, VOUTCM and
the feedback factors β1 and β2. The feedback factors are
simply the portion of the output that is fed back to the input
summing junction by the RFB-RIN resistive voltage divider.
β1 and β2 have the range of zero to one. The VOUTCM term
also includes its offset voltage, VOSCM, and its gain mismatch term, KCM. The KCM term is determined by the
matching of the on-chip RCMP and RCMM resistors in the
common mode level servo (see Figure 2).
While mathematically correct, the basic signal equation
does not immediately yield any intuitive feel for fully
differential amplifier application operation. However, by
nulling out specific terms, some basic observations and
sensitivities come forth. Setting β1 equal to β2, VOSDIFF to
zero and VOUTCM to VOCM gives the old gain equation from
Figure 3. The ground referenced, single-ended input signal equation yields the interesting result that the driven
side feedback factor (β1) has a very different sensitivity
than the grounded side (β2). The CMRR is twice the
feedback factor difference divided by the feedback factor
sum. The differential output offset voltage has two terms.
The first term is determined by the input offset term,
VOSDIFF, and the application’s gain. Note that this term
equates to the formula in Figure 3 when β1 equals β2. The
amount of signal level shifting and the feedback factor
mismatch determines the second term. This term
1992f
35
LTC1992 Family
U
W
U U
APPLICATIO S I FOR ATIO
RFB2
RIN2
– +
–VIN
VINDIFF
+VIN – –VIN
VOCM
RIN1
VOUTDIFF
+VOUT – –VOUT
VOCM LTC1992
+ –
+VIN
+VOUT
–VOUT
RFB1
VOUTDIFF =
2[+VIN • (1 – β1) – (–VIN) • (1 – β2)] + 2VOSDIFF + 2VOUTCM (β1 – β2)
β1 + β2
WHERE:
β1 =
RIN1
RIN2
; β2 =
RIN1 + RFB1
RIN2 + RFB2
; VOSDIFF = AMPLIFIER INPUT REFERRED OFFSET VOLTAGE
VOUTCM = KCM • VOCM + VOSCM
0.999 < KCM < 1.001
• FOR GROUND REFERENCED, SINGLE-ENDED INPUT SIGNAL, LET +VIN = VINSIG AND –VIN = 0V
VOUTDIFF =
2 • VINSIG • (1 – β1) + 2VOSDIFF + 2VOUTCM (β1 – β2)
β1 + β2
• COMMON MODE REJECTION: SET +VIN = –VIN = VINCM, VOSDIFF = 0V, VOUTCM = 0V
CMRR =
∆VINCM
β1 + β2
=2
; OUTPUT REFERRED
β2 – β1
∆VOUTDIFF
• OUTPUT DC OFFSET VOLTAGE: SET +VIN = –VIN = VINCM
VOSDIFFOUT = VOSDIFF
β2 – β1
2
+ (VOUTCM – VINCM) 2
β1 + β2
β1 + β2
Figure 6. Basic Equations for Mismatched or Asymmetrical Feedback Applications Circuits
quantifies the undesired effect of signal level shifting
discussed earlier in the Signal Level Shifting section.
dual, split supply voltage applications with a ground
referenced input signal and a grounded VOCM pin.
Asymmetrical Feedback Application Circuits
The top application circuit in Figure 7 yields a high input
impedance, precision gain of 2 block without any external
resistors. The on-chip common mode feedback servo
resistors determine the gain precision (better than 0.1
percent). By using the –VOUT output alone, this circuit is
also useful to get a precision, single-ended output, high
input impedance inverter. To intuitively understand this
circuit, consider it as a standard op amp voltage follower
(delivered through the signal gain servo) with a complementary output (delivered through the common mode
level servo). As usual, the amplifier’s input common
mode range must not be exceeded. As with a standard op
amp voltage follower, the common mode signal seen at
the amplifier’s input is the input signal itself. This condition limits the input signal swing, as well as the output
signal swing, to be the input signal common mode range
specification.
The basic signal equation in Figure 6 also gives insight to
another piece of intuition. The feedback factors may be
deliberately set to different values. One interesting class of
these application circuits sets one or both of the feedback
factors to the extreme values of either zero or one. Figure 7
shows three such circuits.
At first these application circuits may look to be unstable
or open loop. It is the common mode feedback loop that
enables these circuits to function. While they are useful
circuits, they have some shortcomings that must be
considered. First, do to the severe feedback factor asymmetry, the VOCM level influences the differential output
voltage with about the same strength as the input signal.
With this much gain in the VOCM path, differential output
offset and noise increase. The large VOCM to VOUTDIFF gain
also necessitates that these circuits are largely limited to
The middle circuit is largely the same as the first except
that the noninverting amplifier path has gain. Note that
1992f
36
LTC1992 Family
U
W
U U
APPLICATIO S I FOR ATIO
– +
VOCM
VIN
+VOUT
VOUTDIFF = 2(+VIN – VOCM)
VOCM LTC1992
+ –
–VOUT
SETTING VOCM = 0V
VOUTDIFF = 2VIN
RIN
RFB
– +
VOCM
VIN
VOCM
(
VOUTDIFF = 2 +VIN
1
– VOCM
β
)
;β=
RIN
RIN + RFB
VOCM LTC1992
+ –
–VOUT
– +
+VOUT
SETTING VOCM = 0V
RFB
1
VOUTDIFF = 2VIN β = 2VIN 1 + R
IN
() (
(
VOUTDIFF = 2 +VIN
1–β
+ VOCM
β
)
)
;β=
RIN
RIN + RFB
VOCM LTC1992
RIN
VIN
+VOUT
+ –
–VOUT
RFB
SETTING VOCM = 0V
RFB
1–β
VOUTDIFF = 2VIN β = 2VIN R
IN
( ) ( )
1992 F07
Figure 7. Asymmetrical Feedback Application Circuits (Most Suitable in Applications with Dual,
Split Supplies (e.g., ±5V), Ground Referenced Single-Ended Input Signals and VOCM Connected to Ground)
once the VOCM voltage is set to zero, the gain formula is
the same as a standard noninverting op amp circuit
multiplied by two to account for the complementary
output. Taking RFB to zero (i.e., taking β to one) gives the
same formula as the top circuit. As in the top circuit, this
circuit is also useful as a single-ended output, high input
impedance inverting gain block (this time with gain). The
input common mode considerations are similar to the top
circuit’s, but are not nearly as constrained since there is
now gain in the noninverting amplifier path. This circuit,
with VOCM at ground, also permits a rail-to-rail output
swing in most applications.
The bottom circuit is another circuit that utilizes a standard
op amp configuration with a complementary output. In
this case, the standard op amp circuit has an inverting
configuration. With VOCM at zero volts, the gain formula is
the same as a standard inverting op amp circuit multiplied
by two to account for the complementary output. This
circuit does not have any common mode level constraints
as the inverting input voltage sets the input common mode
level. This circuit also delivers rail-to-rail output voltage
swing without any concerns.
1992f
37
LTC1992 Family
U
TYPICAL APPLICATIO S
Interfacing a Bipolar, Ground Referenced, Single-Ended Signal to a Unipolar Single Supply,
Differential Input ADC (VIN = 0V Gives a Digital Mid-Scale Code)
5V
1µF
0.1µF
40k
10k
13.3k
3
10k
1
7
– +
VMID
2
2.5V
VIN
–2.5V
10k
VOCM
8
0V
2
+IN
100pF
LTC1992
1
8
VREF
VCC
SCK
LTC1864
100Ω
+ –
5V
100Ω
4
3
5
SDO
CONV
–IN
7
6
5
SERIAL
DATA
LINK
GND
6
4
13.3k
1992 TA02a
10k
0.1µF
40k
Compact, Unipolar Serial Data Conversion
5V
1µF
3
0.1µF
1
7
2.5V
VIN
0V
2
8
– +
VMID
VOCM
100Ω
4
2
100pF
LTC1992-2
+ –
+IN
1
8
VREF
VCC
SCK
LTC1864
100Ω
3
5
6
–IN
SDO
CONV
7
6
5
SERIAL
DATA
LINK
GND
4
0.1µF
1992 TA03a
Zero Components, Single-Ended Adder/Subtracter
+VS
0.1µF
VA
VB
VC
1
2
8
3
– +
4
V1 = VB + VC – VA
VOCM LTC1992-2
+ –
6
–VS
5
V2 = VB + VA – VC
0.1µF
1992 TA04
1992f
38
LTC1992 Family
U
TYPICAL APPLICATIO S
Single-Ended to Differential Conversion Driving an ADC
10µF
2.2µF
10Ω
+
3
VREF
5V 10µF
+
36
AVDD
10µF
5V
35
9
AVDD
FFT of the Output Data
+
10
DGND
DVDD
SHDN 33
4
5V
REFCOMP
+
7.5k
2.5V
REF
1.75X
4.375V
CONTROL
LOGIC
AND
TIMING
0.1µF
2
VIN
8
– +
VMID
VOCM
100Ω
LTC1992-1
+ –
6
OVDD 29
1 AIN+
OGND 28
+
100pF
2 AIN–
5
+
1
7
4
µP
CONTROL
LINES
RD 30
BUSY 27
47µF
3
CS 32
CONVST 31
100Ω
–
16-BIT
SAMPLING
ADC
AGND
AGND
5
0.1µF
6
OUTPUT
BUFFERS
B15 TO B0
AGND
7
16-BIT
PARALLEL
BUS
D15 TO D0
fIN = 10.0099kHz
fSAMPLE = 333kHz
0
11 TO 26
AGND VSS
8
5V OR
3V
10µF
AMPLITUDE (dB)
LTC1603
0
–10
– 20
– 30
– 40
– 50
– 60
– 70
– 80
– 90
–100
–110
–120
–130
–140
SNR =85.3dB
THD = –72.1dB
SINAD = –72dB
10 20 30 40 50 60 70 80 90 100
FREQUENCY (kHz)
1992 TA06a
1992 TA06b
34
–5V
–5V
+
10µF
U
PACKAGE DESCRIPTIO
MS8 Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660)
0.889 ± 0.127
(.035 ± .005)
0.254
(.010)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
DETAIL “A”
0° – 6° TYP
GAUGE PLANE
0.53 ± 0.152
(.021 ± .006)
0.42 ± 0.038
(.0165 ± .0015)
TYP
0.65
(.0256)
BSC
1.10
(.043)
MAX
0.86
(.034)
REF
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
8
7 6 5
DETAIL “A”
0.18
(.007)
RECOMMENDED SOLDER PAD LAYOUT
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.65
(.0256)
BSC
0.127 ± 0.076
(.005 ± .003)
0.52
(.0205)
REF
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
MSOP (MS8) 0603
1
2 3
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
4
1992f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
39
LTC1992 Family
U
TYPICAL APPLICATIO
Balanced Frequency Converter (Suitable for Frequencies up to 50kHz)
60kHz LOW PASS FILTER
SAMPLER
2kHz LOWPASS FILTER
5V
0.1µF
9.53k
0.1µF
0.1µF
120pF
9.53k
8.87k
1
7
BNC
9.53k
330pF
2
8.87k
8
VINP
75k
4
3
– +
VMID
4
7
LTC1992
VOCM
11 37.4k
6
1
7
5
12 37.4k
180pF
2
60.4k
8
14
3
– +
VMID
VOCM
CLK –
V
9.53k
+ –
390pF
17
0.1µF
0.1µF
10k
BNC
4
VOUTP
LTC1992
6
16
120pF
60.4k
8
13 1/2 LTC1043
+ –
390pF
V+
BNC
VOUTM
5
75k
0.1µF
0.1µF
VOCM
1992 TA05a
–5V CLK
VINP = 24kHz
(1V/DIV)
0V
CLK = 25kHz
(LOGIC SQUARE WAVE)
(5V/DIV)
VOUTP = 1kHz
(0.5V/DIV)
VOUTM = 1kHz
(0.5V/DIV)
0V
0V
0V
200µs/DIV
1992 TA05b
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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Precision Instrumentation Amplifier
Single Resistor Sets the Gain
LT1990
High Voltage, Gain Selectable Difference Amplifier
±250V Common Mode, Micropower, Selectable Gain = 1, 10
LT1991
Precision Gain Selectable Difference Amplifier
Micropower, Pin Selectable Gain = –13 to 14
LT1995
High Speed Gain Selectable Difference Amplifier
30MHz, 1000V/µs, Pin Selectable Gain = –7 to 8
LT6600-X
Differential In/Out Amplifier Lowpass Filter
Very Low Noise, Standard Differential Amplifier Pinout
1992f
40
Linear Technology Corporation
LT/TP 0105 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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