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.
Figure 14: Phase (I
IN
to V
OUT
)
180
200
R
f
Degrees
220
240
I
IN
0.5pF
V
OUT
50
100
150
Frequency (MHz)
PRELIMINARY DATA SHEET - Rev 1.5
08/2001
7
ANADIGICS [ ANADIGICS, INC ]
