This application note describes how to measure the noise performance of voltage references. The note provides detailed schematics and circuit diagrams of the measurement system and provides instructions on the noise testing method.
The document details a specialized testing scheme designed to measure the extremely low noise of voltage reference devices like the LTC6655. The setup includes a low noise pre-amplifier, filters, and a peak-to-peak noise detector capable of achieving a 160nV noise floor for accurate readout by conventional instruments.
Key design considerations covered include special layout techniques to achieve the required performance, DC stabilization using J-FETs, resistive feedback configurations, and the use of specific components like tantalum capacitors with low leakage. The note also explains how to correct for circuit noise contributions when measuring reference devices.
| Pre-amplifier noise floor | 160nV |
|---|---|
| Forward gain of pre-amplifier | 10^6 |
| Reference voltage (LTC6655) | 2.5V |
| Reference noise (LTC6655) | 775nV |
The pre-amplifier has a noise floor of 160nV, which enables accurate measurement.
It uses a root-sum-square correction switch to account for the circuit's 160nV noise floor when measuring the reference.
The design specifies low dielectric absorption polypropylene capacitors.