Q. What is the typical method of measuring flicker noise using S3245A Noise Amplifier?


A. A typical noise measurement setup and the measurement equipment used for noise measurements were explained in the previous issue of the Simulation Standard.

In order to measure the flicker noise UTMOST III user needs to have a S3245A Noise Amplifier, DC Analyzer, A Dynamic Signal Analyzer (The list of available Dynamic Signal Analyzers were listed in the previous issue) and UTMOST III MOS module.

Prior to the noise measurements or modeling the DC characteristics of the MOS device should be measured. The MOS DC model should be extracted using UTMOST III local or global optimization techniques. The MOS model which is used for DC modeling should include the noise model which is intended for noise parameter extraction. The extracted DC model parameters should be present in the UTMOST III parameter screen.

After the DC model is extracted the Dynamic Signal Analyzer's measurement setup should be defined. A typical hardware settings for noise measurement is presented in Figure1.


The "Run Setup" button should be pressed to load the setup parameters diplayed in the Hardware screen into the Dynamic Signal Analyzer. In order to compensate the noise Amplifier's own noise. The "System Calibration" should be executed prior to the actual flicker noise measurements.

The System Calibrate button is located in the hardware configuration screen for the selected Dynamic Signal Analyzer. During the calibration the S3245A Noise amplifier should be switched on but all other cables should be disconnected from the amplifier. The measured noise level of the amplifier will be stored in UTMOST III and later on it will be subtracted automatically from the measured flicker noise data.

The S3245A Noise Amplifier, DC analyzer and Dynamic Signal Analyzer connection diagram was presented in the previous issue. After making the proper connections the DC bias conditions should be set using the "Measurement Setup" screen for the "Noise" rouitne in UTMOST III. The UTMOST III user should press the "Measure" button in the extraction screen to start the device DC biasing and subsequent flicker noise measurement. The DC analyzer will apply the specified DC voltage to the gate, drain, source and bulk terminals of the MOS device. However, there is a series resistor connected to the drain terminal of the S3245A Noise Amplifier. This series resistor will force the DC analyzer to supply higher external voltage to maintain the specified drain voltage at the device terminal. The noise rouitne in UTMOST III will iterate the external voltage automatically until the proper value is found. The speed of these voltage iterations is limited by the filters connected to the device terminals in the S3245A Noise Amplifier. Therefore the iteration process may take some time. However once the correct external VDS voltage is found the no_bias flag in the fit variable screen can be set to 1 to by-pass the DC voltage iteration process.

After the DC bias is established, UTMOST III will control the Dynamic Signal Analyzer to measure the flicker noise. The measured noise spectra will be transfered to UTMOST III and the data will be displayed in the graphics screen for parameter extraction.


Figure1. A typical settings for a Dynamic Signal Analyzer used for flicker noise measurements.