AD4134 datasheet(61/92 Pages) AD

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Data Sheet

AD4134

APPLICATIONS INFORMATION

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Rev. 0 | 61 of 92

Figure 101. Automatic Gain Control

FRONT-END DESIGN EXAMPLES

The analog front-end circuit of the AD4134 must perform the follow-

ing sequence:

1. Provide adequate input impedance to match the source.

2. Provide reasonably low output impedance to drive the 6 kΩ

differential input resistance of the ADC.

3. Convert the input signal to a balanced, fully differential signal

with fixed common-mode voltage of 2 V to 2.5 V.

4. Provide the necessary gain or attenuation to match the maxi-

mum source signal amplitude to the full-scale input range of the

ADC.

The following low noise amplifiers are recommended for various

types of system challenges. Example operational amplifiers include

the ADA4625-2, ADA4610-2, AD8605, and ADA4075-2. Examples

of fully differential amplifiers include the ADA4940-2, LTC6363,

and ADA4945-1. Example instrumentation amplifiers include the

AD8421 and LTC6373.

Differential Input Signal with Controlled

Common-Mode and High Impedance Source

An example of a high impedance source includes a Wheatstone

bridge type of configuration for strain and pressure monitoring.

The input common mode is well controlled, needing no common-

mode rejection, and a dual op amp configuration works properly.

The circuit in Figure 102 can also provide gain to the signal.

Because of the easy to drive nature of the AD4134, the op amps

do not need to have a high bandwidth and a strong output drive

to overcome kickbacks from traditional ADCs. The ADA4610-2 is

an optimal choice because it offers wide input range, low noise,

suitable bandwidth, and high linearity. The AD8605 is another

optimal choice for rail-to-rail, low voltage, single-supply operation.

Figure 102. Buffered Input with Gain and No Additional Common-Mode

Rejection

Differential Input with Unregulated Common-

Mode Voltage Low Impedance Source

If a wider input common-mode range is required, a fully differential

amplifier can be used, as shown in Figure 103.

Figure 103. Use a Fully Differential Amplifier to Extend Input Common-Mode

Voltage and Signal Gain/Attenuation

This circuit can also provide gain or attenuation of the signal and is

responsible for rejecting the input common mode.

Fully differential amplifiers such as the ADA4940-2, ADA4945-1,

and LTC6363 are all suitable choices. Devices such as the

LTC6363-0.5, LTC6363-1, and LTC6363-2 with a highly matched

integrated resistor network offer unmatched CMRR at 94 dB mini-

mum.

Fully Differential Amplifier with Single Unipolar

Supply

The circuit in Figure 104 offers fixed gain for single-ended or

differential inputs having a low impedance source. Single unipolar 5

V supply operation relaxes the power design.

AD4134 Datasheet(PDF) 61 Page - Analog Devices

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