INTERSIL KAD2708L

KAD2708L
®
Data Sheet
December 5, 2008
8-Bit, 350/275/210/170/105MSPS A/D
Converter
Features
• On-Chip Reference
• Internal Track and Hold
• 1.5VP-P Differential Input Voltage
• 600MHz Analog Input Bandwidth
• Two’s Complement or Binary Output
• Over-Range Indicator
• Selectable ÷2 Clock Divider
• LVDS Compatible Outputs
Applications
• High-Performance Data Acquisition
• Portable Oscilloscope
OVDD
CLKDIV
AVDD3
The Intersil KAD2708L is the industry’s lowest power, 8-bit,
350MSPS, high performance Analog-to-Digital converter. It is
designed with Intersil’s proprietary FemtoCharge™ technology
on a standard CMOS process. The KAD2708L offers high
dynamic performance (48.8dBFS SNR @ fIN = 175MHz) while
consuming less than 330mW. Features include an over-range
indicator and a selectable divide-by-2 input clock divider. The
KAD2708L is one member of a pin-compatible family offering 8
and 10-bit ADCs with sample rates from 105MSPS to
350MSPS and LVDS-compatible or LVCMOS outputs (Table 1).
This family of products is available in 68 Ld RoHS-compliant
QFN packages with exposed paddle. Performance is specified
over the full industrial temperature range (-40°C to +85°C).
AVDD2
FN6813.0
• Medical Imaging
• Cable Head Ends
CLK_P
Clock
Generation
CLK_N
CLKOUTP
• Power-Amplifier Linearization
CLKOUTN
• Radar and Satellite Antenna Array Processing
D7P – D0P
• Broadband Communications
D7N – D0N
8-bit
350MSPS
ADC
INP
S/H
INN
VREF
8
ORP
LVDS
Drivers
1.21 V
VREFSEL
+
–
• Point-to-Point Microwave Systems
ORN
• Communications Test Equipment
2SC
Key Specifications
• SNR = 48.8dBFS at fS = 350MSPS, fIN = 175MHz
VCM
• SFDR = 64dBc at fS = 350MSPS, fIN = 175MHz
AVSS
OVSS
• Power Consumption < 330mW at fS = 350MSPS
Pin-Compatible Family
Ordering Information
PART NUMBER
SPEED
(MSPS)
KAD2708L-35Q68
350
KAD2708L-27Q68
TEMP.
RANGE
(°C)
TABLE 1. PIN-COMPATIBLE PRODUCTS
RESOLUTION, SPEED LVDS OUTPUTS LVCMOS OUTPUTS
PKG.
DWG. #
8 Bits 350MSPS
KAD2708L-35
-40 to +85 68 Ld QFN L68.10x10B
10 Bits 275MSPS
KAD2710L-27
KAD2710C-27
275
-40 to +85 68 Ld QFN L68.10x10B
8 Bits 275MSPS
KAD2708L-27
KAD2708C-27
KAD2708L-21Q68
210
-40 to +85 68 Ld QFN L68.10x10B
10 Bits 210MSPS
KAD2710L-21
KAD2710C-21
KAD2708L-17Q68
170
-40 to +85 68 Ld QFN L68.10x10B
8 Bits 210MSPS
KAD2708L-21
KAD2708C-21
KAD2708L-10Q68
105
-40 to +85 68 Ld QFN L68.10x10B
10 Bits 170MSPS
KAD2710L-17
KAD2710C-17
8 Bits 170MSPS
KAD2708L-17
KAD2708C-17
10 Bits 105MSPS
KAD2710L-10
KAD2710C-10
8 Bits 105MSPS
KAD2708L-10
KAD2708C-10
PACKAGE
NOTE: These Intersil Pb-free plastic packaged products employ
special Pb-free material sets, molding compounds/die attach
materials, and 100% matte tin plate plus anneal (e3 termination finish,
which is RoHS compliant and compatible with both SnPb and Pb-free
soldering operations). Intersil Pb-free products are MSL classified at
Pb-free peak reflow temperatures that meet or exceed the Pb-free
requirements of IPC/JEDEC J STD-020.
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
FemtoCharge is a trademark of Kenet Inc. Copyright Intersil Americas Inc. 2008. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
KAD2708L
Table of Contents
Absolute Maximum Ratings ......................................... 3
Thermal Information...................................................... 3
Electrical Specifications ............................................... 3
Digital Specifications .................................................... 4
Timing Diagram ............................................................. 5
Timing Specifications ................................................... 5
Thermal Impedance....................................................... 5
ESD ................................................................................. 5
Pin Description .............................................................. 6
Pin Configuration .......................................................... 7
Typical Performance Curves ........................................ 8
Functional Description ................................................. 11
Reset ..........................................................................
Voltage Reference......................................................
Analog Input ...............................................................
Clock Input .................................................................
Jitter............................................................................
Digital Outputs ............................................................
11
11
11
12
12
13
Equivalent Circuits........................................................ 13
Layout Considerations ................................................. 14
Split Ground and Power Planes .................................
Clock Input Considerations.........................................
Bypass and Filtering ...................................................
LVDS Outputs ............................................................
Unused Inputs ............................................................
14
14
14
14
14
Definitions...................................................................... 14
Package Outline Drawing ............................................. 15
L68.10x10B ................................................................ 15
2
FN6813.0
December 5, 2008
KAD2708L
Absolute Maximum Ratings
Thermal Information
AVDD2 to AVSS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.4V to 2.1V
AVDD3 to AVSS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.4V to 3.7V
OVDD2 to OVSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.4V to 2.1V
Analog Inputs to AVSS. . . . . . . . . . . . . . . . . -0.4V to AVDD3 + 0.3V
Clock Inputs to AVSS. . . . . . . . . . . . . . . . . . -0.4V to AVDD2 + 0.3V
Logic Inputs to AVSS (VREFSEL, CLKDIV) -0.4V to AVDD3 + 0.3V
Logic Inputs to OVSS (RST, 2SC) . . . . . . . . -0.4V to OVDD2 + 0.3V
VREF to AVSS . . . . . . . . . . . . . . . . . . . . . . . -0.4V to AVDD3 + 0.3V
Analog Output Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA
Logic Output Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA
LVDS Output Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA
Operating Temperature . . . . . . . . . . . . . . . . . . . . . . .-40°C to +85°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +150°C
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and
result in failures not covered by warranty.
Electrical Specifications All specifications apply under the following conditions unless otherwise noted: AVDD2 = 1.8V, AVDD3 = 3.3V,
OVDD = 1.8V, TA = -40°C to +85°C (typical specifications at +25°C), fSAMPLE = 350MSPS, 270MSPS,
210MSPS, 170MSPS and 105MSPS, fIN = Nyquist at -0.5dBFS.
KAD2708L-35
PARAMETER
KAD2708L-27
KAD2708L-21
KAD2708L-17
KAD2708L-10
SYMBOL CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS
DC SPECIFICATIONS
Analog Input
Full-Scale Analog
Input Range
VFS
Full Scale Range
Temp. Drift
AVTC
Common-Mode
Output Voltage
VCM
1.4
Full Temp
1.5
1.6
1.4
1.5
1.6
1.4
1.5
1.6
1.4
1.5
1.6
1.4
1.5
1.6
VP-P
257
230
210
198
176
ppm/°C
860
860
860
860
860
mV
Power Requirements
1.8V Analog
Supply Voltage
AVDD2
1.7
1.8
1.9
1.7
1.8
1.9
1.7
1.8
1.9
1.7
1.8
1.9
1.7
1.8
1.9
V
3.3V Analog
Supply Voltage
AVDD3
3.15
3.3
3.45 3.15
3.3
3.45 3.15
3.3
3.45 3.15
3.3
3.45 3.15
3.3
3.45
V
1.8V Digital
Supply Voltage
OVDD
1.7
1.8
1.9
1.8
1.9
1.8
1.9
1.8
1.9
1.8
1.9
V
1.8V Analog
Supply Current
IAVDD2
51
60
44
51
38
42
35
39
29
33
mA
3.3V Analog
Supply Current
IAVDD3
50
54
41
45
33
37
28
32
21
24
mA
1.8V Digital
Supply Current
IOVDD
39
44
34
39
33
36
31
36
28
32
mA
PD
327
365
275
310
237
263
211
241
172
196
mW
Power
Dissipation
1.7
1.7
1.7
1.7
AC SPECIFICATIONS
Maximum
Conversion Rate
fS MAX
Minimum
Conversion Rate
fS MIN
350
275
50
210
50
170
50
105
50
MSPS
50
MSPS
Differential
Nonlinearity
DNL
-0.3 ±0.2
fIN = 10MHz
(for -17 and -10
versions only)
0.4
-0.3 ±0.2
0.4
-0.3 ±0.2
0.4
-0.3 ±0.2
0.4
-0.3 ±0.2
0.4
LSB
Integral
Nonlinearity
INL
-0.8 ±0.2
fIN = 10MHz
(for -17 and -10
versions only)
0.8
-0.8 ±0.2
0.8
-0.8 ±0.2
0.8
-0.8 ±0.2
0.8
-0.8 ±0.2
0.8
LSB
3
FN6813.0
December 5, 2008
KAD2708L
Electrical Specifications All specifications apply under the following conditions unless otherwise noted: AVDD2 = 1.8V, AVDD3 = 3.3V,
OVDD = 1.8V, TA = -40°C to +85°C (typical specifications at +25°C), fSAMPLE = 350MSPS, 270MSPS,
210MSPS, 170MSPS and 105MSPS, fIN = Nyquist at -0.5dBFS. (Continued)
KAD2708L-35
PARAMETER
KAD2708L-27
KAD2708L-21
KAD2708L-17
KAD2708L-10
SYMBOL CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS
Signal-to-Noise
Ratio
SNR
Signal-to-Noise
and Distortion
SINAD
Effective Number
of Bits
ENOB
Spurious-Free
Dynamic Range
SFDR
Two-Tone SFDR
fIN = 10MHz
49.0
50.4
49.5
49.5
49.5
dBFS
fIN = Nyquist
46.5 48.8
46.5 49.2
46.5 49.2
46.5 49.2
46.5 49.2
dBFS
fIN = 430MHz
48.0
49.0
49.1
49.1
49.1
dBFS
fIN = 10MHz
48.9
49.2
49.5
49.5
49.5
dBFS
fIN = Nyquist
46.5 48.2
46.5 49.2
46.5 49.2
46.5 49.2
46.5 49.2
dBFS
fIN = 430MHz
47.7
48.9
48.9
49.0
48.9
dBFS
fIN = 10MHz
7.8
7.9
7.9
7.9
7.9
Bits
7.9
Bits
fIN = Nyquist
7.4
7.9
7.4
7.9
7.4
7.9
7.4
7.9
7.4
fIN = 430MHz
7.6
7.8
7.8
7.8
7.8
Bits
fIN = 10MHz
65.0
67.6
69.1
69.1
69.1
dBc
69.1
dBc
fIN = Nyquist
61
64
61
66.6
61
69.1
61
69.1
61
fIN = 430MHz
62
66.1
69.0
69.0
68.9
dBc
2TSFDR fIN = 133MHz,
135MHz
61
63
65
65
65
dBc
Word Error Rate
WER
10-12
10-12
10-12
10-12
10-12
Full Power
Bandwidth
FPBW
600
600
600
600
600
MHz
Digital Specifications
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
INPUTS
High Input Voltage (VREFSEL)
VREFSEL VIH
Low Input Voltage (VREFSEL)
VREFSEL VIL
Input Current High (VREFSEL)
VREFSEL IIH
VIN = AVDD3
Input Current Low (VREFSEL)
VREFSEL IIL
VIN = AVSS
High Input Voltage (CLKDIV)
CLKDIV VIH
Low Input Voltage (CLKDIV)
CLKDIV VIL
Input Current High (CLKDIV)
CLKDIV IIH
VIN = AVDD3
25
Input Current Low (CLKDIV)
CLKDIV IIL
VIN = AVSS
0
High Input Voltage (RST,2SC)
RST,2SC VIH
0.8*AVDD3
V
0.2*AVDD3
V
0
1
10
µA
25
65
75
µA
0.8*AVDD3
V
0.2*AVDD3
V
65
75
µA
1
10
µA
0.8*OVDD2
V
Low Input Voltage (RST,2SC)
RST,2SC VIL
0.2*OVDD2
V
Input Current High (RST,2SC)
RST,2SC IIH
VIN = OVDD
0
1
10
µA
Input Current Low (RST,2SC)
RST,2SC IIL
VIN = OVSS
25
50
75
µA
Input Capacitance
CDI
CLKP, CLKN P-P Differential Input Voltage
VCDI
CLKP, CLKN Differential Input Resistance
RCDI
10
MΩ
CLKP, CLKN Common-Mode Input Voltage
VCCI
0.9
V
3
0.5
pF
3.6
VP-P
LVDS OUTPUTS
Differential Output Voltage
VT
210
mV
VOS
1.15
V
Output Rise Time
tR
500
ps
Output Fall Time
tF
500
ps
Output Offset Voltage
4
FN6813.0
December 5, 2008
KAD2708L
Timing Diagram
Sample N
INP
INN
tA
CLKN
CLKP
L
tPID
CLKOUTN
CLKOUTP
tPCD
tPH
D[7:0]P
D[7:0]N
Data N-L
Data N-L+1
Data N
invalid
FIGURE 1. LVDS TIMING DIAGRAM
Timing Specifications
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
Aperture Delay
tA
1.7
ns
RMS Aperture Jitter
jA
200
fs
Input Clock to Data Propagation Delay
tPID
3.5
Data Hold Time
tPH
-300
Output Clock to Data Propagation Delay
6.5
ns
ps
tPCD
2.8
L
28
cycles
tOVR
1
cycle
Latency (Pipeline Delay)
Overvoltage Recovery
5.0
3.7
ns
Thermal Impedance
PARAMETER
SYMBOL
TYP
UNIT
θJP
30
°C/W
Junction to Paddle (Note 1)
NOTE:
1. Paddle soldered to ground plane.
ESD
Electrostatic charge accumulates on humans, tools and
equipment and may discharge through any metallic package
contacts (pins, balls, exposed paddle, etc.) of an integrated
circuit. Industry-standard protection techniques have been
utilized in the design of this product. However, reasonable
care must be taken in the storage and handling of ESD
sensitive products. Contact Intersil for the specific ESD
sensitivity rating of this product.
5
FN6813.0
December 5, 2008
KAD2708L
Pin Description
PIN NUMBER
NAME
1, 14, 18, 20
AVDD2
2, 7, 10, 19, 21, 24
AVSS
Analog Supply Return
3
VREF
Reference Voltage Out/In
4
VREFSEL
5
VCM
6, 15, 16, 25
AVDD3
3.3V Analog Supply
8, 9
INP, INN
Analog Input Positive, Negative
11-13, 29-36, 62, 63, 67
DNC
17
CLKDIV
22, 23
CLKN, CLKP
26, 45, 61
OVSS
27, 41, 44, 60
OVDD2
28
RST
37, 38
D0N, D0P
LVDS Bit 0 (LSB) Output Complement, True
39, 40
D1N, D1P
LVDS Bit 1 Output Complement, True
42, 43
CLKOUTN, CLKOUTP
LVDS Clock Output Complement, True
46, 47
D2N, D2P
LVDS Bit 2 Output Complement, True
48, 49
D3N, D3P
LVDS Bit 3 Output Complement, True
50, 51
D4N, D4P
LVDS Bit 4 Output Complement, True
52, 53
D5N, D5P
LVDS Bit 5 Output Complement, True
54, 55
D6N, D6P
LVDS Bit 6 Output Complement, True
56, 57
D7N, D7P
LVDS Bit 7 Output Complement, True
58, 59
ORN, ORP
Over-Range Complement, True
64-66
FUNCTION
1.8V Analog Supply
Reference Voltage Select (0:Int 1:Ext)
Common-Mode Voltage Output
Do Not Connect
Clock Divide by Two (Active Low)
Clock Input Complement, True
Output Supply Return
1.8V LVDS Supply
Power On Reset (Active Low)
Connect to OVDD2
68
2SC
Exposed Paddle
AVSS
6
Two’s Complement Select (Active Low)
Analog Supply Return
FN6813.0
December 5, 2008
KAD2708L
2SC
DNC
OVDD2
OVDD2
OVDD2
DNC
DNC
OVSS
OVDD2
ORP
ORN
D7P
D7N
D6P
D6N
D5P
D5N
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
Pin Configuration
AVDD2
1
51
D4P
AVSS
2
50
D4N
VREF
3
49
D3P
VREFSEL
4
48
D3N
VCM
5
47
D2P
AVDD3
6
46
D2N
AVSS
7
KAD2708L
45
OVSS
44
OVDD2
43
CLKOUTP
68 QFN
42
CLKOUTN
INP
8
INN
9
AVSS
10
DNC
11
41
OVDD2
DNC
12
40
D1P
DNC
13
39
D1N
38
D0P
37
D0N
Top View
Not to Scale
21
22
23
24
25
26
27
28
29
30
31
32
33
34
AVSS
CLKP
AVSS
AVDD3
OVSS
OVDD2
RST
DNC
DNC
DNC
DNC
DNC
DNC
DNC
CLKN
DNC
35
20
36
17
AVDD2
16
19
AVDD3
CLKDIV
18
15
AVSS
14
AVDD3
AVDD2
AVDD2
FIGURE 2. PIN CONFIGURATION
7
FN6813.0
December 5, 2008
KAD2708L
Typical Performance Curves
AVDD2 = OVDD2 = 1.8V, AVDD3 = 3.3V, TA = +25°C, fSAMPLE = 350MHz, fIN = 175MHz,
AIN = -0.5dBFS unless noted.
-50
70
SFDR
-60
HD 2, HD3((dBc)
dBc
S N R( d B F S ), S FD R ( d Bc)
B
-55
65
60
55
-65
HD3
-70
-75
50
-80
SNR
HD2
45
-85
-90
40
5
105
205
305
f IN (M Hz)
405
5
505
10 5
205
3 05
f IN( MHz)
405
505
FIGURE 4. HD2 AND HD3 vs fIN
FIGURE 3. SNR AND SFDR vs fIN
80
70
HD3
-30
60
HD2, HD3 (dBc)
dBc
S N R (d B F S ) , S F D R (dBc)
(d
-20
-40
SNR
50
-50
HD2
-60
40
SFDR
-70
30
-80
-30
20
-30
-2 5
-20
-1 5
A IN ( d B F S )
-1 0
-5
0
-25
-20
-15
-10
-5
0
300
350
Input Amplitude (dBFS)
FIGURE 5. SNR AND SFDR vs AIN
FIGURE 6. HD2 AND HD3 vs AIN
80
-65
76
-70
68
HD2, HD3(dBc)
SNR(dBFS), SFDR (dBc)
SFDR
72
64
60
56
52
-75
HD3
-80
-85
48
HD2
SNR
44
-90
40
50
100
150
200
250
f SA MP LE (fS ) (MSPS)
FIGURE 7. SNR AND SFDR vs fSAMPLE
8
300
350
50
100
150
200
250
fSAMPLE (MSPS)
FIGURE 8. HD2 AND HD3 vs fSAMPLE
FN6813.0
December 5, 2008
KAD2708L
Typical Performance Curves
AVDD2 = OVDD2 = 1.8V, AVDD3 = 3.3V, TA = +25°C, fSAMPLE = 350MHz, fIN = 175MHz,
AIN = -0.5dBFS unless noted. (Continued)
1
350
POWER DISSIPATION (PD) (mW)
330
0.75
310
0.5
290
DNL (LSB s)
270
250
230
210
0.25
0
-0.25
-0.5
190
170
-0.75
150
100
150
200
250
fSAMPLE (fS ) (MSPS)
300
-1
0
350
32
64
96
128
CODE
160
192
224
255
FIGURE 10. DIFFERENTIAL NONLINEARITY vs OUTPUT CODE
FIGURE 9. POWER DISSIPATION vs fSAMPLE
50,000
1
45,000
0.7 5
40,000
35,000
CODE COUNT
INL (LS Bs)
0.5
0.2 5
0
-0.2 5
30,000
25,000
20,000
15,000
-0.5
10,000
-0.7 5
-1
5,000
0
32
64
96
128
CODE
160
1 92
2 24
0
124
25 5
125
FIGURE 11. INTEGRAL NONLINEARITY vs OUTPUT CODE
HD3 = -69dBc
-80
-40
SINAD = 49.4dBFS
HD2 = -81dBc
-60
HD3 = -91dBc
-80
-100
-100
-120
0
SFDR = 69.2dBc
AMPLITUDE (dB)
AMPLITUDE (dB)
-60
130
SNR = 49.4dBFS
-20
SFDR = 68.4dBc
HD2 = -86dBc
129
Ain = -0.47dBFS
SNR = 49.4dBFS
SINAD = 49.3dBFS
128
0
Ain = -0.47dBFS
-40
127
CODE
FIGURE 12. NOISE HISTOGRAM
0
-20
126
20
40
60
80
FREQUENCY (MHz)
100
120
FIGURE 13. OUTPUT SPECTRUM @ 9.865MHz
9
-120
0
20
40
60
80
FREQUENCY (MHz)
100
120
FIGURE 14. OUTPUT SPECTRUM @ 133.805MHz
FN6813.0
December 5, 2008
KAD2708L
Typical Performance Curves
AVDD2 = OVDD2 = 1.8V, AVDD3 = 3.3V, TA = +25°C, fSAMPLE = 350MHz, fIN = 175MHz,
AIN = -0.5dBFS unless noted. (Continued)
0
0
Ain = -0.48dBFS
Ain = -7.1dBFS
SNR = 49.3dBFS
-20
-20
2TSF DR = 67dBc
IMD3 = -74dBFS
SINAD = 49.1dBFS
-40
AMPLIT UDE (dB)
AMPLITUDE (dB)
SFDR = 63dBc
HD2 = -63dBc
HD3 = -67dBc
-60
-80
-60
-80
-100
-100
-120
-40
0
20
40
60
80
FREQUENCY (MHz)
100
-120
120
0
FIGURE 15. OUTPUT SPECTRUM @ 299.645MHz
20
40
60
80
FREQUENCY (MHz)
0
Ain = -7dBFS
Ain = -7dBFS
2TSFD R = 63dBc
-20
2TSF DR = 73dBc
-20
IMD3 = -76dBFS
IMD3 = -81dBFS
-40
AMPLITUDE (dB)
AMPLIT UDE (dB)
-40
-60
-60
-80
-80
-100
-100
0
20
40
60
80
FREQUENCY (MHz)
100
-120
120
FIGURE 17. TWO-TONE SPECTRUM @ 140MHz, 141MHz
0
20
40
60
80
FREQUENCY (MHz)
100
120
FIGURE 18. TWO-TONE SPECTRUM @ 300MHz, 305MHz
75
700
70
SFDR
600
65
500
60
tCAL(ms)
SNR(dBFS), SFDR(dBc)
120
FIGURE 16. TWO-TONE SPECTRUM @ 69MHz, 70MHz
0
-120
100
55
400
300
50
200
SNR
45
40
-40
-20
0
20
40
AMBIENT TEMPERATURE, C
60
FIGURE 19. SNR AND SFDR vs TEMPERATURE
10
80
100
100 125 150 175 200 225 250 275 300 325 350
f SAMPLE (f S) (MSPS)
FIGURE 20. CALIBRATION TIME vs fS
FN6813.0
December 5, 2008
KAD2708L
Functional Description
Voltage Reference
The KAD2708L is an eight bit, 350MSPS A/D converter in a
pipelined architecture. The input voltage is captured by a
sample and hold circuit and converted to a unit of charge.
Proprietary charge-domain techniques are used to compare
the input to a series of reference charges. These
comparisons determine the digital code for each input value.
The converter pipeline requires 24 sample clocks to produce
a result. Digital error correction is also applied, resulting in a
total latency of 28 clock cycles. This is evident to the user as
a latency between the start of a conversion and the data
being available on the digital outputs.
The VREF pin is the full-scale reference, which sets the fullscale input voltage for the chip and requires a bypass
capacitor of 0.1µF or larger.An internally generated
reference voltage is provided from a bandgap voltage buffer.
This buffer can sink or source up to 50µA externally.
At start-up, a self-calibration is performed to minimize gain
and offset errors. The reset pin (RST) is initially held low
internally at power-up and will remain in that state until the
calibration is complete. The clock frequency should remain
fixed during this time.
An external voltage may be applied to this pin to provide a
more accurate reference than the internally generated
bandgap voltage or to match the full-scale reference among
a system of KAD2708L chips. One option in the latter
configuration is to use one KAD2708L's internally generated
reference as the external reference voltage for the other
chips in the system. Additionally, an externally provided
reference can be changed from the nominal value to adjust
the full-scale input voltage within a limited range.
Calibration accuracy is maintained for the sample rate at
which it is performed, and therefore should be repeated if the
clock frequency is changed by more than 10%. Recalibration
can be initiated via the RST pin, or power cycling, at any
time.
To select whether the full-scale reference is internally
generated or externally provided, the digital input port
VREFSEL should be set appropriately, low for internal or
high for external.This pin also has an internal 18kΩ pull-up
resistor. To use the internally generated reference VREFSEL
can be tied directly to AVSS, and to use an external
reference VREFSEL can be left unconnected.
Reset
Analog Input
Recalibration of the ADC can be initiated at any time by
driving the RST pin low for a minimum of one clock cycle. An
open-drain driver is recommended.
The fully differential ADC input (INP/INN) connects to the
sample and hold circuit. The ideal full-scale input voltage is
1.5VP-P, centered at the VCM voltage of 0.86V as shown in
Figure 22.
The calibration sequence is initiated on the rising edge of
RST, as shown in Figure 21. The over-range output (ORP) is
set high once RST is pulled low, and remains in that state
until calibration is complete. The ORP output returns to
normal operation at that time, so it is important that the
analog input be within the converter’s full-scale range in
order to observe the transition. If the input is in an overrange state the ORP pin will stay high and it will not be
possible to detect the end of the calibration cycle.
While RST is low, the output clock (CLKOUTP/CLKOUTN)
stops toggling and is set low. Normal operation of the output
clock resumes at the next input clock edge (CLKP/CLKN)
after RST is deasserted. At 350MSPS the nominal
calibration time is ~190ms.
CLKN
CLKP
Calibration Time
RST
Calibration Begins
V
1.8
1.4
0.75V
INN
INP
VCM
1.0
0.86V
0.6
-0.75V
0.2
t
FIGURE 22. ANALOG INPUT RANGE
Best performance is obtained when the analog inputs are
driven differentially. The common-mode output voltage,
VCM, should be used to properly bias each input as shown
in Figures 23 and 24. An RF transformer will give the best
noise and distortion performance for wideband and/or high
intermediate frequency (IF) inputs. Two different transformer
input schemes are shown in Figures 23 and 24.
ORP
Calibration Complete
CLKOUTP
FIGURE 21. CALIBRATION TIMING
11
FN6813.0
December 5, 2008
KAD2708L
Clock Input
0.01µF
Analog
In
Ω
50O
KAD2708
VCM
ADT1-1WT
ADT1-1WT
0.1µF
The clock input circuit is a differential pair (see Figure 29).
Driving these inputs with a high level (up to 1.8VP-P on each
input) sine or square wave will provide the lowest jitter
performance. The recommended drive circuit is shown in
Figure 26. The clock can be driven single-ended, but this will
reduce the edge rate and may impact SNR performance.
Ω
1kO
Ω
1kO
FIGURE 23. TRANSFORMER INPUT, GENERAL APPLICATION
AVDD2
CLKP
1nF
ADTL1-12
Analog
Input
ADTL1-12
Ω
25O
1nF
KAD2708
1nF
1nF
Clock
Input
200O
Ω
VCM
Ω
25O
FIGURE 26. RECOMMENDED CLOCK DRIVE
FIGURE 24. TRANSFORMER INPUT, HIGH IF APPLICATION
A back-to-back transformer scheme is used to improve
common-mode rejection, which keeps the common-mode
level of the input matched to VCM. The value of the
termination resistor should be determined based on the
desired impedance.
The sample and hold circuit design uses a switched
capacitor input stage, which creates current spikes when the
sampling capacitance is reconnected to the input voltage.
This creates a disturbance at the input which must settle
before the next sampling point. Lower source impedance will
result in faster settling and improved performance. Therefore
a 1:1 transformer and low shunt resistance are
recommended for optimal performance.
A differential amplifier can be used in applications that
require DC coupling, at the expense of reduced dynamic
performance. In this configuration the amplifier will typically
reduce the achievable SNR and distortion performance. A
typical differential amplifier configuration is shown in
Figure 25.
Ω
348O
Ω
69.8O
CLKN
TC4-1W
0.1µF
Ω
25O
Use of the clock divider is optional. The KAD2708L's ADC
requires a clock with 50% duty cycle for optimum
performance. If such a clock is not available, one option is to
generate twice the desired sampling rate, then use the
KAD2708L's divide-by-2 to generate a 50%-duty-cycle clock.
This frequency divider uses the rising edge of the clock, so
50% clock duty cycle is assured. Table 2 describes the
CLKDIV connection.
TABLE 2. CLKDIV PIN SETTINGS
CLKDIV PIN
DIVIDE RATIO
AVSS
2
AVDD
1
CLKDIV is internally pulled low, so a pull-up resistor or logic
driver must be connected for undivided clock.
Jitter
In a sampled data system, clock jitter directly impacts the
achievable SNR performance. The theoretical relationship
between clock jitter and maximum SNR is shown in
Equation 1 and illustrated in Figure 27.
1
SNR = 20 log 10 ⎛ --------------------⎞
⎝ 2πf t ⎠
100O
Ω
(EQ. 1)
IN J
+
Vin
-
151O
Ω
0.22µF
CM
VCM
Ω
100O
Ω
49.9O
25O
Ω
Ω
69.8O
Ω
348O
KAD2708
0.1µF
Where tJ is the RMS uncertainty in the sampling instant.
This relationship shows the SNR that would be achieved if
clock jitter were the only non-ideal factor. In reality,
achievable SNR is limited by internal factors such as
differential nonlinearity aperture jitter and thermal noise.
FIGURE 25. DIFFERENTIAL AMPLIFIER INPUT
12
FN6813.0
December 5, 2008
KAD2708L
Any internal aperture jitter combines with the input clock jitter
in a root-sum-square fashion since they are not statistically
correlated, and this determines the total jitter in the system.
The total jitter, combined with other noise sources, then
determines the achievable SNR.
10 0
95
tj=0.1 ps
90
14 Bits
SN R - dB
85
80
tj=1 ps
12 Bits
75
Digital Outputs
70
tj=10 p s
65
60
Data is output on a parallel bus with LVDS-compatible
drivers.
1 0 Bits
tj=1 00 ps
55
The output format (Binary or Two’s Complement) is selected
via the 2SC pin as shown in Table 3.
50
1
10
1 00
1 00 0
In put Fr equen cy - MH z
TABLE 3. 2SC PIN SETTINGS
FIGURE 27. SNR vs CLOCK JITTER
2SC PIN
MODE
AVSS
Two’s Complement
AVDD (or unconnected)
Binary
Equivalent Circuits
AVDD2
A VD D3
IN P
Φ
F1
C sam p
0.3pF
Φ
F2
To
C harge
Pipeline
AVDD2
To Clock
Generation
CLKP
AV D D 3
IN N
2pF
Φ
F1
C sam p
0.3pF
Φ
F2
To
C harge
Pipeline
AVDD2
CLKN
FIGURE 28. ANALOG INPUTS
FIGURE 29. CLOCK INPUTS
OVDD
OVDD
DATA
DATA
D[7:0]P
OVDD
D[7:0]N
DATA
DATA
FIGURE 30. LVDS OUTPUTS
13
FN6813.0
December 5, 2008
KAD2708L
Layout Considerations
Split Ground and Power Planes
Data converters operating at high sampling frequencies
require extra care in PC board layout. Many complex board
designs benefit from isolating the analog and digital
sections. Analog supply and ground planes should be laid
out under signal and clock inputs. Locate the digital planes
under outputs and logic pins. Ground planes, if separated,
should be joined at the exposed paddle under the chip.
Clock Input Considerations
Use matched transmission lines to the inputs for the analog
input and clock signals. Locate transformers, drivers and
terminations as close to the chip as possible.
Bypass and Filtering
Aperture Jitter is the RMS variation in aperture delay for a
set of samples.
Clock Duty Cycle is the ratio of the time the clock wave is at
logic high to the total time of one clock period.
Differential Non-Linearity (DNL) is the deviation of any
code width from an ideal 1 LSB step.
Effective Number of Bits (ENOB) is an alternate method of
specifying Signal to Noise-and-Distortion Ratio (SINAD). In
dB, it is calculated as: ENOB = (SINAD - 1.76)/6.02.
Integral Non-Linearity (INL) is the deviation of each individual
code from a line drawn from negative full-scale (1/2 LSB below
the first code transition) through positive full-scale (1/2 LSB
above the last code transition). The deviation of any given code
from this line is measured from the center of that code.
Bulk capacitors should have low equivalent series resistance.
Tantalum is a good choice. For best performance, keep
ceramic bypass capacitors very close to device pins. Longer
traces will increase inductance, resulting in diminished
dynamic performance and accuracy. Make sure that
connections to ground are direct and low impedance.
Least Significant Bit (LSB) is the bit that has the smallest
value or weight in a digital word. Its value in terms of input
voltage is VFS/(2N-1) where N is the resolution in bits.
LVDS Outputs
Most Significant Bit (MSB) is the bit that has the largest
value or weight. Its value in terms of input voltage is VFS/2.
Output traces and connections must be designed for 50Ω
(100Ω differential) characteristic impedance. Keep traces
direct, and minimize bends where possible. Avoid crossing
ground and power-plane breaks with signal traces.
Unused Inputs
The RST and 2SC inputs are internally pulled up, and can be
left open-circuit if not used.
CLKDIV is internally pulled low, which divides the input clock
by two.
VREFSEL is internally pulled up. It must be held low for
internal reference, but can be left open for external
reference.
Definitions
Analog Input Bandwidth is the analog input frequency at
which the spectral output power at the fundamental
frequency (as determined by FFT analysis) is reduced by
3dB from its full-scale low-frequency value. This is also
referred to as Full Power Bandwidth.
Aperture Delay or Sampling Delay is the time required
after the rise of the clock input for the sampling switch to
open, at which time the signal is held for conversion.
Missing Codes are output codes that are skipped and will
never appear at the ADC output. These codes cannot be
reached with any input value.
Pipeline Delay is the number of clock cycles between the
initiation of a conversion and the appearance at the output
pins of the corresponding data.
Power Supply Rejection Ratio (PSRR) is the ratio of a
change in power supply voltage to the input voltage
necessary to negate the resultant change in output code.
Signal to Noise-and-Distortion (SINAD) is the ratio of the
RMS signal amplitude to the RMS sum of all other spectral
components below one half the clock frequency, including
harmonics but excluding DC.
Signal-to-Noise Ratio (SNR) (without Harmonics) is the
ratio of the RMS signal amplitude to the RMS sum of all
other spectral components below one-half the sampling
frequency, excluding harmonics and DC.
Spurious-Free-Dynamic Range (SFDR) is the ratio of the
RMS signal amplitude to the RMS value of the peak spurious
spectral component. The peak spurious spectral component
may or may not be a harmonic.
Two-Tone SFDR is the ratio of the RMS value of either input
tone to the RMS value of the peak spurious component. The
peak spurious component may or may not be an IMD product.
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
14
FN6813.0
December 5, 2008
KAD2708L
Package Outline Drawing
L68.10x10B
68 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE
Rev 0, 11/08
PIN 1
INDEX AREA
6
10.00
A
4X 8.00
B
52
PIN 1
INDEX AREA
6
68
51
1
35
17
64X 0.50
Exp. DAP
7.70 Sq.
10.00
0.15 (4X)
34
18
68X 0.55
68X 0.25
4
TOP VIEW
0.10 M C A B
BOTTOM VIEW
SEE DETAIL "X"
0.90 Max
8.00 Sq
C
0.10 C
0.08 C
SEATING PLANE
64X 0.50
SIDE VIEW
68X 0.25
9.65 Sq
C
7.70 Sq
0 . 2 REF
5
0 . 00 MIN.
0 . 05 MAX.
68X 0.75
DETAIL "X"
TYPICAL RECOMMENDED LAND PATTERN
NOTES:
1.
Dimensions are in millimeters.
Dimensions in ( ) for Reference Only.
2. Dimensioning and tolerancing conform to AMSEY14.5m-1994.
3. Unless otherwise specified, tolerance : Decimal ± 0.05
4. Dimension b applies to the metallized terminal and is measured
between 0.15mm and 0.30mm from the terminal tip.
5. Tiebar shown (if present) is a non-functional feature.
6. The configuration of the pin #1 identifier is optional, but must be
located within the zone indicated. The pin #1 identifier may be
either a mold or mark feature.
15
FN6813.0
December 5, 2008