AD8368 datasheet(13/20 Pages) AD

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AD8368

Rev. A | 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

VGAIN 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:

GainHIGH

(dB) = 37.5 × VGAIN − 14

GainLOW

(dB) = −38 × VGAIN + 24.8

where VGAIN is expressed in volts.

–15

–10

–5

–4

–3

–2

–1

0.8

0.6

0.4

0.2

VGAIN (V)

GAIN_H

GAIN_L

ERROR_H

ERROR_L

Figure 32. Gain and Conformance Error vs. VGAIN

As shown in Figure 32, the gain function can be either an

increasing or decreasing function of VGAIN, depending on the

MODE pin.

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