AD4134 datasheet(31/92 Pages) AD

31 / 92 page

Data Sheet

AD4134

THEORY OF OPERATION

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Rev. 0 | 31 of 92

ANALOG FRONT-END DESIGN

SIMPLIFICATION

The result from the two major benefits of the CTSD architecture

described in the Easy to Drive Input and Reference section and the

Inherent Antialiasing Filter (AAF) section is a major simplification

of the analog front-end design of the precision medium bandwidth

data acquisition signal chain.

Figure 63 shows the analog front-end circuit for a discrete time

ADC. For discrete time ADC, in between the precision instrumenta-

tion amplifier and the ADC is a third-order antialiasing filter plus an

ADC driving circuit based on a fully differential ADC driving amplifi-

er. An additional RC circuit is required at the ADC input to ensure

stability of the driver and to help further suppress the kickback. A

reference driving circuit based on an operation amplifier is placed

between the reference IC and the ADC. The circuit incorporates

a second-order low-pass filter to help reduce the wideband noise

from the reference source.

Figure 64 shows the signal chain of the AD4134. For the continu-

ous time-based AD4134, the easy to drive and inherent antialiasing

property results in significant simplification of the analog front-end

design. Other than the apparent area and cost saving, the front-end

simplification also removes the noise, error, and instability intro-

duced by the removed circuit, improving the overall performance

of the signal chain. As shown in Figure 64, the instrumentation

amplifier can directly drive the resistive inputs of the AD4134,

and the bandwidth of the amplifier adds to the antialias rejection,

making the signal chain an alias free signal chain.

Figure 63. Example Analog Front-End Circuit Design of the Discrete Time-Based ADC

Figure 64. Example Analog Front-End Circuit Design of the AD4134

AD4134 Datasheet(PDF) 31 Page - Analog Devices