High Speed Differential Amplifier FEATURES Dual Wavelength Slew R

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High Speed Differential Amplifier FEATURES Dual Wavelength Slew R

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SP8126
High Speed Differential Amplifier
FEATURES Dual Wavelength Slew Rate 250V/µs Fast Settling Time Gain Control Output Swing Offset Voltage: 10mV Offset Drift: 20µV/°C 12dB External Gain Adjust Range
GAIN RGCOM
SP8126
VOUT VOUT RGAIN2 RGAIN1
APPLICATIONS DVDRW DVDRAM CDRW
DESCRIPTION SP8126 high-speed, differential output amplifier that integrates photodiode adjustable gain block chip. Independent gain control allows individual adjustment 780mn 650nm wavelength operation, found CD/DVD optical storage drives. This allows user control laser power system high-speed DVDRW, DVDRAM CDRW systems. wide output swing also allows better system performance, through improved dynamic range.
GAIN
Buffer
VOUT+ 1VP-P (Depend FPC) 50pF
Gain Control
(Flexible Flat Cable)
Dummy
Buffer
VOUT1VP-P 50pF
RGCOM
RGAIN1
RGAIN2
Figure Functional Diagram Typical Application
Rev. 6/02/03 SP8126 High Speed Differential Amplifier Copyright 2003 Sipex Corporation
ABSOLUTE MAXIMUM RATINGS
TJ(MAX) 120°C VS(MAX) VIN(MAX) Power Supply Voltage Continuous Power Dissipation (TAMB 70°C) (derate 13.3mW/°C above +70°C) 90mW These stress ratings only functional operation device these ratings other above those indicated operation sections specifications below implied. Exposure absolute maximum rating conditions extended periods time affect reliability.
ELECTRICAL SPECIFICATIONS
Unless otherwise noted: 5.0V, CLOAD 50pF GND, RLOADP RLOADN GND, RGAIN (Nominal Gain), -20°C +85°C, Output measured differentially.
PARAMETER Supply Voltage Output Sensitivity Input Optical Power Required Produce Output Swing Full Scale Linear Output Voltage Swing Output Common Mode Voltage
CONDITIONS
3000 Vcc/2
3600
UNITS
Laser Beam Diameter 0.70mm, 2400 uniform density 4.5V 5.5V Vcc/2.2 RGAIN 1230 (High Gain) RGAIN 1230 (High Gain)
Vcc/1.8
µV/C µV/C mVrms mVrms
Output Offset Voltage
Output Offset Voltage Drift
Output Noise
100MHz 100MHz, RGAIN 1230 (High Gain)
Bandwidth
-3dB -3dB, RGAIN 1230 (High Gain)
PSRR
4.5V 5.5V 4.5V 5.5V, RGAIN 1230 (High Gain)
Output Settling Time Final Value) Output Slew Rate Output Overshoot
Rev. 6/02/03
2VPP Step 2VPP Step, RGAIN 1230 (High Gain) 2VPP Step
SP8126 High Speed Differential Amplifier
V/µs
Copyright 2003 Sipex Corporation
ELECTRICAL SPECIFICATIONS: Continued
Unless otherwise noted: 5.0V, CLOAD 50pF GND, RLOADP RLOADN GND, RGAIN (Nominal Gain), -20°C +85°C, Output measured differentially.
PARAMETER Power Supply Current
CONDITIONS
UNITS
-20°C +85°C Gain Adjust Range Gain Select Input Voltage (TTL Level) Gain Select Input Voltage (TTL Level) RGAIN 1230
DESCRIPTION
NUMBER NAME GAIN RGCOM RGAIN1 RGAIN2 VOUTVOUT+ FUNCTION Supply Voltage Gain Select Common connection point RGAIN1 RGAIN2 Power Ground Gain Adjust (Gain Select LOW) OPEN Gain Adjust (Gain Select HIGH) Output Voltage Output Voltage
THEORY OPERATION Internal Operation SP8126 circuit integrated photo detector designed with nominal sensitivities 3mV/µW both 650nm 780nm wavelength laser light. part's sensitivity also adjusted continuously independently different gain modes external resistors over range ±6dB. gain modes controlled compatible logic input, called GAIN SELECT. This logic selects between external gain setting resistors allow independent control settings gain functions. system stage design, consisting Trans-Impedance Amplifier (TIA) output buffer stage. dark condition outputs VOUT- VOUT+ reference voltage
Rev. 6/02/03
that defined internally Vcc/2. With 650nm 780nm wavelength laser light falling photodetector, output will swing differentially around Vcc/2 proportional with light power according chosen gain. Gain control first stage differential used convert photodetector current balanced differential voltage. traditional fixed feedback resistors have been replaced with active resistor circuit that sets trans-impedance value. Resistor Control Block that senses value external gain setting resistor controls value equivalent feedback resistor.
Copyright 2003 Sipex Corporation
SP8126 High Speed Differential Amplifier
THEORY OPERATION: Continued ±6dB Gain adjustment therefore done directly TIA, adjusting active feedback blocks proportional with gain setting resistor. external resistor directly signal path, therefore parasitic from off-chip connections does affect signal quality. value active feedback controlled tightly over supply temperature changes through Control Block with active feedback circuitry. Gain control proportional with external resistor, lowest value RGAIN will produce -6dB gain adjustment highest value will produce +6dB gain adjustment. Please consult specification table required RGAIN values. Buffer This stage buffers differential signal from VOUT pins refers signal internal reference voltage. balanced current feedback amplifier used this purpose achieve high slew rate fast settling. buffer designed drive high capacitive loads. maximum load 50pF bulk. actual load typically flexible printed circuit (FPC) that acts like transmission line. This presents distributed capacitive load plus inductance resistance. this case care should taken match characteristic impedance line avoid standing waves ringing. buffer designed drive ground. However, this resistor adjusted value accommodate characteristic impedance signal trace. output buffer amplifier designed stable without load with loads 50pF lumped capacitance.
11.0k 10.0k 9.0k 8.0k 7.0k
(V/W)
6.0k 5.0k 4.0k 3.0k 2.0k 1.0k 0.0k 1.0k 1.5k 2.0k 2.5k 3.0k
RGAIN
Figure Sensitivity
180M
-9.5dB
160M 140M 120M
-6.0dB
0.0dB
(Hz)
100M
.0dB
9.5dB
1.0k
1.5k
2.0k
2.5k
RGAIN
Figure SP8126 Bandwidth versus RGAIN
TABLE SYSTEM GUARANTEED TARGET GAIN POINTS. VOUTP-VOUTN 2VP-P, 27°C
Gain (dB) Sensitivity (V/W) RGAIN (nS) (MHz) (µW) Specification
+9.5 -9.5
Rev. 6/02/03
9000 6000 3000 1500 1000
2300 1230
1331 1988
Target Guaranteed Guaranteed Guaranteed Target
SP8126 High Speed Differential Amplifier
Copyright 2003 Sipex Corporation
LAYOUT ROUTING CONSIDERATIONS major consideration developing optical pick-up head system extremely small form factor, which additionally aggravated physical locations required light path. Special care must taken when designing Flex this part. output peak current requirement order 12.5mA when driving 50pF capacitive load with slew rate 250V/µs Therefore care must taken provide inductance, resistance paths power ground output traces. Supply coupling also very important. Good supply decoupling important ensure high frequency performance system eliminating supply lead inductance effects. decoupling capacitor shown Figure should close part possible. This capacitor should 0.1µF ceramic. optional improve decoupling recommended tantalum. layout pictured here. Note wide short traces supply lines. traces gain resistors RGAIN1 RGAIN2 kept short possible avoid excessive parasitics. parasitics these nodes will limit performance system. RGAIN1 RGAIN2 subminiature potentiometers application. This single layer board using material. order minimize coupling capacitance into gain setting resistor nodes, also critical that VOUT+ VOUT- routed away from traces associated with gain-setting resistors.
Figure Test Evaluation Layout Lead Package
Bottom
Rev. 6/02/03
SP8126 High Speed Differential Amplifier
Copyright 2003 Sipex Corporation
0.1µF GAIN GAIN RGCOM VOUT+ VOUTRGAIN2 RGAIN1
VOUT+
50pF
SP8126
50pF
VOUTRG1
Figure Test Evaluation Schematic
Rev. 6/02/03
SP8126 High Speed Differential Amplifier
Copyright 2003 Sipex Corporation
PACKAGE:
0.090
0.600
VIEW
SIDE VIEW
BOTTOM VIEW
SIDE VIEW
DIMENSIONS Minimum/Maximum
8-PIN 0.90/1.10 .127/.33 0.30/0.50 0.50 2.90/3.10 3.00/3.20 0.75 3.40/3.60 0.40/0.60 0.28/0.48 0.075/0.275
DETECTOR SIZE
0.35mm
0.70mm
Detector Area
(3.5mm 3.0mm)
Rev. 6/02/03
SP8126 High Speed Differential Amplifier
Copyright 2003 Sipex Corporation
ORDERING INFORMATION
Part Number Temperature Range Package Type
SP8126 -20°C +85°C lead (3.0mm 3.5mm) SP8126EB -20°C +85°C lead (3.0mm 3.5mm)
Corporation
ANALOG EXCELLENCE
Sipex Corporation Headquarters Sales Office South Hillview Drive Milpitas, 95035 TEL: (408) 934-7500 FAX: (408) 935-7600
Sales Office Linnell Circle Billerica, 01821 TEL: (978) 667-8700 FAX: (978) 670-9001 e-mail: sales@sipex.com
Sipex Corporation reserves right make changes products described herein. Sipex does assume liability arising application product circuit described herein; neither does convey license under patent rights rights others. Rev. 6/02/03 SP8126 High Speed Differential Amplifier Copyright 2003 Sipex Corporation

High Speed Differential Amplifier FEATURES Dual Wavelength Slew R

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