Application NoteAnalog

Frequency Domain Response of Switched-Capacitor ADCs

Characterizes the input impedance of switched-capacitor ADCs like the AD9236 and provides methods for designing optimized interfaces using network analyzer measurements.

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Overview

AN-742 details a methodology for measuring and understanding the frequency-dependent input impedance of pipeline ADCs featuring switched-capacitor front ends. Focusing on the AD9236, the document explains the impedance differences between track and hold modes and how these variations affect interface design. It provides a measurement setup using a network analyzer and S-parameters to determine differential impedance. The note also addresses time-domain 'kickback' glitches and includes a practical design example using a transformer-coupled input with inductive matching to achieve a 50-ohm termination and improve common-mode rejection.

Use Cases

Designing analog front-end interfaces for pipeline ADCs
Impedance matching for high-speed data converters
Characterizing ADC input response using network analyzers
Calculating transformer-coupled input filters for ADCs
Minimizing signal distortion caused by ADC kickback

Topics

switched-capacitor ADC

input impedance

AD9236

track and hold mode

S-parameters

impedance matching

network analyzer

differential input

pipeline ADC

AD9229

AD9235

AD9238

Referenced Parts

Analog Devices

describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.

Analog Devices

describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.

Analog Devices

All measurements and model calculations were made using the AD9236 in a 32-lead chip scale package (CSP).

Analog Devices

describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.

Analog Devices

describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.

Analog Devices

describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.

AD9229	Analog Devices	describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.
AD9235	Analog Devices	describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.
AD9236	Analog Devices	All measurements and model calculations were made using the AD9236 in a 32-lead chip scale package (CSP).
AD9238	Analog Devices	describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.
AD9245	Analog Devices	describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.
AD9248	Analog Devices	describing the general behavior of this switched-capacitor ADC family, including the AD9229, AD9235, AD9238, AD9245, and AD9248.

Frequency Domain Response of Switched-Capacitor ADCs | Design Resources