PRELIMINARY DATA SHEET - Rev 1.5

08/2001

7

ATA00501

AGC Capacitor

It is important to select an external AGC capacitor of

high quality and appropriate size. The ATA00501D1C

has an on-chip 70 KW resistor with a shunt 4 pF

capacitor to ground. Without external capacitance

the chip will provide an AGC time constant of 280

nS. For the best performance in a typical 51MB/s

SONET receiver, a minimum AGC capacitor of 56pF

is recommended. This will provide the minimum

amount of protection against pattern sensitivity and

pulse width distortion on repetitive data sequences

during high average optical power conditions.

Conservative design practices should be followed

when selecting an AGC capacitor, since unit to unit

variability of the internal time constant and various

data conditions can lead to data errors if the chosen

value is too small.

Phase Response

At frequencies below the 3dB bandwidth of the

device, the transimpedance phase response is

characteristic of a single pole transfer function (as

shown in the Phase vs Frequency curve). The output

impedance is essentially resistive up to 1000 MHz.

50

100

150

Frequency (MHz)

I

IN

0.5pF

V

OUT

180

200

220

240

R

f