CN-0261 is a reference circuit designed and built by Analog Devices for quick and easy system integration to help solve today's analog, mixed-signal, and RF design challenges.
This document is a Circuit Note (CN-0261) from Analog Devices detailing a reference circuit designed to optimize AC performance in an 18-bit, 250 kSPS PulSAR measurement system. The solution centers on the AD7691 ADC, driven by an AD8597 ultralow distortion amplifier and referenced to an ADR435 voltage source.
The circuit achieves a Signal-to-Noise Ratio (SNR) of 101 dB and Total Harmonic Distortion (THD) of -118 dB with a 1 kHz input tone. The document provides the simplified schematic, component descriptions including power supply requirements (+8V/−2V), and details on evaluation boards like EVAL-CN0261-SDPZ used for testing.
| Sampling Rate | 250 kSPS |
|---|---|
| SNR (Signal-to-Noise Ratio) | 101 dB |
| THD (Total Harmonic Distortion) | -118 dB |
| Power Supply Voltage (VDD) | +8 V / -2 V |
The heart of this circuit is the AD7691, an 18-bit, 250 kSPS charge redistribution, successive approximation, analog-to-digital converter (ADC).
The AD7691 is driven directly from the AD8597 ultralow distortion, ultralow noise amplifier.
The circuit uses the ADR435 as an ultralow noise 5 V reference.