Datasheet

AD8368
Rev. B | Page 13 of 20
GAIN CONTROL INTERFACE
The AD8368 has a linear-in-dB gain control interface that can
be operated in either a gain-up mode or gain-down mode. In
the gain-up mode with the MODE pin pulled high, the gain
increases with increasing gain voltages. In the gain-down mode,
with the MODE pin pulled low, the gain decreases with increasing
gain voltages. In both modes of operation, the gain control
slope is maintained at +37.5 dB/V or −38 dB/V (depending
on mode selection) over temperature, supply, and process as
V
GAIN
varies from 100 mV to 900 mV. To form an AGC loop
with the on-board detector around the VGA, the MODE pin
has to be pulled low.
The gain functions for MODE pulled high and low are given
respectively by
Gain
HIGH
(dB) = 37.5 × V
GAIN
− 14
Gain
LOW
(dB) = −38 × V
GAIN
+ 24.8
where
V
GAIN
is expressed in volts.
25
–15
–10
–5
0
5
10
15
20
4
–4
–3
–2
–1
0
1
2
3
010.80.60.40.2
GAIN (dB)
V
GAIN
(V)
05907-035
.0
GAIN_H
GAIN_L
ERROR_H
ERROR_L
CONFORMANCE ERROR (dB)
Figure 32. Gain and Conformance Error vs. V
GAIN
As shown in Figure 32, the gain function can be either an
increasing or decreasing function of V
GAIN
, depending on the
MODE pin.