ATA06211
AGC Capacitor
It is important to select an external AGC capacitor of
high quality and appropriate size. The ATA06211D1C
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 622 MB/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.
180
200
Rf
VOUT
220
240
IIN
0.5pF
50
100
150
Frequency (MHz)
Figure 12: Phase (IIN to VOUT)
7
PRELIMINARY DATA SHEET - Rev 4
08/2001
ANADIGICS [ ANADIGICS, INC ]
