CS5374 datasheet(16/44 Pages) CIRRUS

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CS5374

DS862F1

AMPLIFIER OPERATION

The CS5374 high-impedance, low-noise CMOS

differential input, differential output amplifiers are

optimized for precision analog signals between DC

and 2 kHz. They have multiplexed inputs and pro-

grammable gains of 1x, 2x, 4x, 8x, 16x, 32x, and

64x. The performance of this amplifier makes it

ideal for low-frequency, high-dynamic-range ap-

plications requiring low distortion and minimal

power consumption.

3.1 Amplifier Inputs — INA, INB

The amplifier analog inputs are designed for high-

impedance differential hydrophone sensors and so

have very low input bias below 1 pA.

3.1.1

Multiplexer Settings

— MUX

Input multiplexing simplifies system connections

by providing separate inputs for a sensor and test

DAC (INA, INB) as well as an internal termination

for noise tests. The multiplexer determines which

input is connected to the amplifier, and is set

through internal configuration registers accessed

through the SPI port, see the “SPITM Register Sum-

mary” on page 34 for more information.

Although a mux selection is provided to enable the

INA and INB switches simultaneously, significant

current should not be driven through them in this

mode. The CS5374 mux switches will maintain

good linearity only with minimal signal current.

3.1.2

Gain Settings

— GAIN

The CS5374 supports gain ranges of 1x, 2x, 4,x 8x,

16x, 32x, and 64x. Amplifier gain is selected using

internal configuration registers accessed through

the SPI port, see the “SPITM Register Summary”

on page 34 for more information.

3.2 Amplifier Outputs — OUTR, OUTF

The amplifier analog outputs are externally sepa-

rated into rough / fine charge signals to connect

into the modulator inputs. Each differential output

requires two series resistors and a differential ca-

pacitor to create the modulator anti-alias RC filter.

3.2.1

Guard Output — GUARD

The GUARD pin outputs the common mode volt-

age of the selected analog signal input. It can be

used to drive the cable shield between a high-im-

pedance sensor and the amplifier inputs. Driving

the cable shield with the analog signal common

mode voltage minimizes leakage and improves sig-

nal integrity from high-impedance sensors.

The GUARD output is defined as the midpoint

voltage between the + and – halves of the currently

INA1+

INB1+

MUX1

INB1-

INA1-

GUARD1

OUT1+ OUT1-

Figure 13. CS5374 Amplifier Block Diagram

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