SIPEX SP8026

®
SP8024/8025/8026
Advanced
200V/µs Integrated APC Amplifier
with Gain Adjust & Differential Output
FEATURES
■ Slew Rate of 200V/µs
■ Fast Settling Time - 10ns
■ Gain Switch
■ 2V Output Swing
■ Low Offset Voltage: < 10mV
■ Low Offset Drift: < 20µV/°C
■ 12dB External Gain Adjust Range
VCC
1
GAIN
2
RCOM
3
GND
4
SP8024/25/26
8 Pin COB
8
VOUT +
7
VOUT -
6
RGAIN2
5
RGAIN1
DESCRIPTION
The SP8024, SP8025, and SP8026 are high-speed, differential output APC amplifiers that
integrate the photodiode and adjustable gain block on one chip. This allows the user to control
the laser power of the system in high-speed DVDRW, DVDRAM and CDRW systems. The wide
2V output swing also allows better system performance.
FUNCTIONAL DIAGRAM
GAIN
VCC
2463
VOUT+
Buffer
GND
31
850
31
Rf1
Rf2
TIA
1VP-P
50pF
1k
(Flexible Flat Cable)
850
VOUTBuffer
1VP-P
2463
RG1
Rev. 6/02/03
1k
RGAIN2
RGAIN1
RGCOM
50pF
RG2
SP8024, 25, 26 200V/µs Integrated APC Amplifier
1
© Copyright 2003 Sipex Corporation
ABSOLUTE MAXIMUM RATINGS
TJ(MAX) ........................................................................................ 120°C
VS(MAX) ............................................................................................... 6V
VIN(MAX) .............................................................................................. 6V
These are stress ratings only and functional operation
of the device at these ratings or any other above those
indicated in the operation sections of the specifications
below is not implied. Exposure to absolute maximum
rating conditions for extended periods of time may
affect reliability.
ELECTRICAL SPECIFICATIONS
Unless otherwise noted: VCC = +5.0V, CLOAD = 50pF to GND, RGAIN=262Ω and RLOAD = 1kΩ. -20°C≤TA≤ +85°C,
nominal gain
PARAMETER
CONDITIONS
Supply Voltage
Nominal Output Sensitivity
SP8024
SP8025
SP8026
Any Select Mode
ODB Gain
Input Optical Power Required
to Produce 2 V Output Swing
SP8024
SP8025
SP8026
Any Select Mode
ODB Gain
Full Scale Output Voltage Swing(Vp-p)
MIN
TYP
4.5
5
1.9
Output Common Mode Voltage
MAX UNITS
5.5
V
1000
2000
3000
V/W
2
1
0.666
mW
2
V
VCC/2
V
Differential Output Offset Voltage
-10
10
mV
Differential Output Offset Voltage Drift
-20
20
µV/°C
1
2
mV
3
5
Differential Output Noise
BW: 1kHz to 1MHz
Differential Output Noise
BW: 1kHz to 100MHz
Differential Output Slew Rate
200
Differential Output Settling Time
to 1% of Final Value, 2V Step
250
10
Output Overshoot, 2V step
Bandwidth (-3db)
PSRR
4.5V < VCC < 5.5V
Power Supply Current
TA = 25°C
Full Temp No Load
Gain Adjust Range
< 5% Overshoot,
150 < RGAIN < 1350Ω
Input Voltage
Vlow(TTL Level)
Vhigh(TTL Level)
Rev. 6/02/03
2
ns
5
%
100
60
65
dB
20
mA
MHz
25
-9
75
SP8024, 25, 26 200V/µs Integrated APC Amplifier
15
65
2.2
TJA, 3mm x 3.5mm Package
mV
V/µs
3
dB
0.8
V
V
°C/W
© Copyright 2003 Sipex Corporation
PIN DESCRIPTION
PIN NUMBER
NAME
FUNCTION
1
VCC
2
GAIN
Gain Select
3
RCOM
Common connection point for RGAIN1 and RGAIN2
4
GND
Power Ground
5
RGAIN1
Gain Adjust 1
6
RGAIN2
Gain Adjust 2
7
VOUT-
Output Voltage -
8
VOUT+
Output Voltage +
Supply Voltage
THEORY OF OPERATION
Internal Operation
The SP8024/25/26 APC circuits have an integrated photo detector and are designed with
three nominal sensitivities of 1mV/µW, 2mV/
µW and 3mV/µW respectively. Each part’s sensitivity can also be adjusted continuously and
independently for two different gain modes via
two external resistors over a range of 12dB. The
two gain modes are controlled by a TTL compatible logic input. This logic input also normalizes the internal photo detector’s responsivity
for 650nm and 780nm laser wavelengths. The
logic pin selects between the two external gain
setting resistors to allow independent control
and settings for the two gain functions.
The 8024 APC family uses two stages of gain to
optimize for speed and offset. The two stages
consist of a differential trans-impedance amplifier (TIA), and a differential gain adjust amplifier.
Variable Gain Amplifier
This stage is used to vary the gain of the system.
It provides selection for two different gain setting resistors, RGAIN1 and RGAIN2, at pins 5 and
6 via internal MOSFET switches S1 and S2. The
logic input at pin 2 controls the selection of the
two external gain set resistors.
Table 1: Gain Select Logic Truth Table
Rexternal,
Pin 3 to:
Gain
Factor (x)
Sensitivity
(mV/µW)
RG1 = RG2 = 262Ω
0 or Open
RG1 - Pin 5
6.25
1
2
3
1
RG2 - Pin 6
6.25
1
2
3
SP8024
SP8025
SP8026
The gain of this balanced amplifier topology is
given by:
TIA
The first stage is a differential trans-impedance
amplifier (TIA) for converting the photo detector output current to a balanced differential
voltage. This topology allows for fast settling of
the photo detector and also cancels offset effects. The TIA has no external components.
Rev. 6/02/03
Gain
Select
Pin 2
GAIN = 1 +
Rf1 + Rf2
REXT
where RGAIN is external and Rf1 = Rf2 = 850Ω
in feedback.
The nominal gain is defined as 6.25.
SP8024, 25, 26 200V/µs Integrated APC Amplifier
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© Copyright 2003 Sipex Corporation
THEORY OF OPERATION : Continued
Variable Gain Amplifier: continued
There are internal buffering resistors and a
MOSFET switch resistance in series with the
external Rgain. These internal resistances add
up to a nominal value of 62Ω. Therefore the true
gain equation is:
GAIN = 1 +
with the internal compensation of the amplifier,
instability occurs. This instability appears as overshoot in the transient response. The stray capacitance at pins 5 and 6 should be kept below 1pF.
This stage also allows the part to drive high
capacitive loads. The maximum load capacitance is 50pF bulk. The actual load is typically
a flexible ribbon cable (FLEX) that acts like a
transmission line. This presents a distributed
capacitive load plus inductance and resistance.
In this case care should be taken to match the
characteristic impedance of the line at the far
end to avoid standing waves and ringing. The
buffer is designed to drive 1kΩ to ground. However, this resistor can be adjusted in value to
accommodate the characteristic impedance of
the signal trace.
Rf1 + Rf2
REXT + 62
This gives a nominal external Rgain value of
324 - 62 = 262Ω for a gain of 6.25.
The constraints on this stage are the parasitic
capacitances associated with the input pins. The
resistors used for setting the system gain are
actually subminiature potentiometers. They are
used for calibrating out systematic variations in
the optical path.
Pins 5 and 6 connect to the summing node of the
gain stage through MOSFET switches. When a
capacitor is added to the summing node of an
inverting amplifier it creates a pole in the response. If this pole increases enough to interfere
6.0
5.0
4.0
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
-9.0
-10.0
-11.0
-12.0
REXT
RGAIN
Sensitivity
0
200
400
600
800
1000
1200
1400
1600
1800
2000
6.0
5.7
5.3
5.0
4.7
4.3
4.0
3.7
3.3
3.0
2.7
2.3
2.0
1.7
1.3
1.0
0.7
0.3
0.0
2200
System Sensitivity (mV/µW)
Gain (dB)
SP8026 Differential APC Sensitivity
versus Gain Set Resistor
Resistance (Ω)
Figure 1. System Gain versus Gain Set Resisitor
Rev. 6/02/03
SP8024, 25, 26 200V/µs Integrated APC Amplifier
4
© Copyright 2003 Sipex Corporation
Layout and Routing Considerations
Special care must be taken when designing the
Flex or PCB for this part. The output peak
current requirement is in the order of 12.5mA
when driving 50pF of capacitive load with a
slew rate of 200V/s Therefore care must be
taken to provide low inductance, low resistance
paths for power and ground and output traces.
Supply coupling is also very important. Good
supply decoupling is important to ensure the
high frequency performance of the system by
eliminating supply lead inductance effects. The
decoupling capacitor C1 should be as close to
the part as possible. This capacitor should be
0.1µF ceramic. C2 is optional to improve
decoupling and is recommended to be 1µF tan-
talum. The layout of the PCB is pictured here.
Note the wide and short traces on the supply
lines.
The traces for the gain resistors R1 and R2 are
kept as short as possible to avoid excessive
parasitics. Any parasitics on these nodes will
limit the performance of the system. R1 and R2
are subminiature potentiometers in the application. This is a single layer board done on FR4
material.
In order to minimize coupling capacitance into
the gain setting resistor nodes, it is also critical
that VOUT+ and VOUT- are routed away from the
traces associated with the gain-setting resistors.
Top
Bottom
Figure 2. Test and Evaluation PCB Layout for COB 8 Lead Package
Rev. 6/02/03
SP8024, 25, 26 200V/µs Integrated APC Amplifier
5
© Copyright 2003 Sipex Corporation
+5V
VOUT+
+
C1
0.1µF
RL1
1k
VCC
GAIN
GAIN
RGCOM
GND
1
2
3
4
CL1
50pF
VOUT+
8
SP8024
SP8025
SP8026
+
VOUT-
7
RGAIN2
6
RL2
1k
+
CL2
50pF
RGAIN1
5
VOUTRG1
262
RG2
262
Figure 3. Test and Evaluation Schematic
Rev. 6/02/03
SP8024, 25, 26 200V/µs Integrated APC Amplifier
6
© Copyright 2003 Sipex Corporation
PACKAGE : 8 PIN COB
0.090
1
8
2
7
3
6
4
5
b
0.600
D
e
F
S
L
H
PIN
SIDE VIEW
TOP VIEW
BOTTOM VIEW
E
2X)
DIMENSIONS in
mm
Minimum/Maximum
5° (
B
A
C
SIDE VIEW
DETECTOR SIZE
8–PIN
COB
A
0.90/1.10
B
.127/.33
b
0.30/0.50
c
0.50 nom
D
2.90/3.10
E
3.00/3.20
e
0.75 nom
H
3.40/3.60
L
0.40/0.60
F
0.28/0.48
S
0.075/0.275
0.35mm
0.70mm
8 PIN COB
(3.5mm x 3.0mm)
Detector Area
Rev. 6/02/03
SP8024, 25, 26 200V/µs Integrated APC Amplifier
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© Copyright 2003 Sipex Corporation
ORDERING INFORMATION
Part Number
Temperature Range
Package Type
SP8024 ................................................... -20°C to +85°C .............. 8 lead COB (3.0mm x 3.5mm)
SP8025 ................................................... -20°C to +85°C .............. 8 lead COB (3.0mm x 3.5mm)
SP8026 ................................................... -20°C to +85°C .............. 8 lead COB (3.0mm x 3.5mm)
Corporation
ANALOG EXCELLENCE
Sipex Corporation
Headquarters and
Sales Office
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
FAX: (408) 935-7600
Sales Office
22 Linnell Circle
Billerica, MA 01821
TEL: (978) 667-8700
FAX: (978) 670-9001
e-mail: [email protected]
Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the
application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.
Rev. 6/02/03
SP8024, 25, 26 200V/µs Integrated APC Amplifier
8
© Copyright 2003 Sipex Corporation