CS3170 Datasheet, PDF (2/11 Pages) Applied Micro Circuits Corporation – 2.5 Gbps Transimpedance Amplifier

S3170 – 2.5 Gbps Transimpedance Amplifier
Revision A – August 12, 2004
Data Sheet
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 V_CC.
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, C_FILT.
This bandwidth corresponds to the low frequency -3 dB
cutoff of the TIA. Increasing the value of C_FILT will
reduce the low frequency -3 dB cutoff. With no C_FILT
capacitor added it will be at 45 kHz.
Figure 2. S3170 Detailed Block Diagram
Vcc
RBYPASS
VCC
100 Ω
IIN
1500 Ω
C_FILT
(OPTIONAL)
FILT
BIAS
X 6.7
OUTP
OUTN
GND
2
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