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GAINProfile

SYNC

SignalInput

to AFE5801

Holdtimeat

stopgain,

Rampdownfrom

stopgaintostart

gain, trd

Waittime

atstartgain

Rampuptimefrom

startgaintostopgain,

tru

Waittime

atstartgain

SyncPeriod

SyncPeriod = tru + th + trd + tw

External

System

Signal

AFE5801

SLOS591D – SEPTEMBER 2008 – REVISED MAY 2010

www.ti.com

Figure 38. SYNC Period

Non-Uniform Gain Increment Mode

In the non-uniform gain increment mode, the user sets an arbitrary shape for the gain versus time curve. For a

given time/sampling instant, the digital gain setting is obtained from an internal memory of 148 positions/registers

(named REG_VALUEs), each 9 bits wide, loaded by the user through the serial port (see Serial Interface

section). Addresses 1 to 148 can be used to access these registers, while TGC_REGISTER_WREN = 1.

As explained above, the most significant bit of each register (REG_VALUE<8>) denotes either increment or

decrement gain from current gain value. The other 8 bits (REG_VALUE<7:0>) denote the time (a multiple of 8 ×

Tclk, being Tclk the sampling clock) for the change of the gain from the CURRENT_GAIN to CURRENT_GAIN

±1dB (depending on the REG_VALUE<8>). The fastest ramp (shortest time) for this 1dB gain change is set by

REG_VALUE<7:0> equal to 0x00 and it is 8 × Tclk. The slowest ramp (longest time) for this 1dB gain change is

set by REG_VALUE<7:0> equal to 0xFF and it is 255 × 8 × Tclk.

INTERP_ENABLE sets the way the gain is increased/decreased. By default the gain ramp is implemented in

steps of 1dB (INTERP_ENABLE equal to 0). If INTERP_ENABLE is equal to 1, the actual 1dB gain step is

implemented in 8 steps of 0.125dB.

The 148 REG_VALUE registers can be used to store either a single curve or multiple TGC curves. The

START_INDEX register points to the REG_VALUE register where the TGC curve starts and the STOP_INDEX

STOP_INDEX registers the desired TGC curves can be chosen.

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