CS3170 datasheet(2/11 Pages) AMCC

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AMCC Confidential and Proprietary

Revision A – August 12, 2004

Data Sheet

S3170 – 2.5 Gbps Transimpedance Amplifier

DETAILED DESCRIPTION

Figure 2 depicts the overall block diagram of the

S3170 transimpedance amplifier. The amplifier cir-

cuitry consists of a transimpedance stage and an

output driver stage with a 16 dB gain. The transimped-

ance amplifier converts the photodiode photocurrent to

a voltage. The photodiode can be biased by connect-

ing it to the RBYPASS pin or it can be connected

directly to VCC.

The amplifier gain is linear for an input of up to 125 µA.

Above that the output stage limits. The output voltage

is limited at 1000 mV, differential, peak to peak.

The output of the transimpedance stage is converted

to a differential signal by the combination of the output

stage and a bias block. This bias block averages the

output of the transimpedance stage and establishes

the DC input reference for the output stage. The band-

width of this circuit is set by an on-chip capacitor, but

can be reduced by adding an off-chip capacitor, CFILT.

This bandwidth corresponds to the low frequency -3 dB

cutoff of the TIA. Increasing the value of CFILT will

reduce the low frequency -3 dB cutoff. With no CFILT

capacitor added it will be at 45 kHz.

Figure 2. S3170 Detailed Block Diagram

VCC

GND

RBYPASS

IIN

OUTP

OUTN

FILT

BIAS

FILT

(OPTIONAL)

100

Ω

Vcc

1500

Ω

X 6.7

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