AD9600 datasheet(33/73 Pages) AD

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AD9600

Rev. B | Page 32 of 72

Increment Gain (IG) and Decrement Gain (DG)

The increment gain and decrement gain indicators are intended

to be used together to provide information to enable external gain

control. The decrement gain indicator works in conjunction with

the coarse upper threshold bits, asserting when the input

magnitude is greater than the 3-bit value in the coarse upper

threshold register (Address 0x105). The increment gain indicator,

similarly, corresponds with the fine lower threshold bits, except

that it is asserted only if the input magnitude is less than the

value programmed in the fine lower threshold register after the

dwell time elapses. This dwell time is set by the 16-bit increase

gain dwell time register (Address 0x10A and Address 0x10B) and

is in units of ADC input clock cycles ranging from 1 to 65,535. The

fine lower threshold register is a 13-bit register that is compared

with the magnitude at the output of the ADC. This comparison

is subject to the ADC clock latency but allows a finer, more

accurate comparison. The fine threshold magnitude is defined

in Equation 1 (see the Fine Upper Threshold (F_UT) section).

The decrement gain output is influenced by the fast detect output

pins, which provide a fast indication of potential overrange

conditions. Assertion of the increment gain indicator is based

on the comparison at the output of the ADC, requiring the input

magnitude to remain below an accurate, programmable level for a

predefined period before signaling external circuitry to increase

the gain.

The operation of the IG and DG indicators is shown in Figure 66.

UPPER THRESHOLD (COARSE OR FINE)

FINE LOWER THRESHOLD

F_LT

C_UT OR F_UT*

DWELL TIME

TIMER RESET BY

RISE ABOVE F_LT

TIMER COMPLETES BEFORE

SIGNAL RISES ABOVE F_LT

NOTE: OUTPUTS FOLLOW THE INSTANTANEOUS SIGNAL LEVEL AND NOT THE ENVELOPE BUT ARE GUARANTEED ACTIVE FOR A MINIMUM OF TWO ADC CLOCK CYCLES.

*C_UT AND F_UT DIFFER ONLY IN ACCURACY AND LATENCY.

DWELL TIME

Figure 66. Threshold Settings for C_UT, F_UT, F_LT, IG, and DG

AD9600 Datasheet(PDF) 33 Page - Analog Devices