Give these tests a try on your favorite amplifier and compare your results to the respective product data sheet. These are easy DC tests to run when you are trying to understand how the amplifier reacts to the different power supply, common-mode input voltage, and output voltage conditions. You can change the voltage of V 2 to meet the conditions in Table 1. Table 1 V OS, PSRR, CMRR, and A OL test guidance for Figure 1 circuit. It is equal to, V OS = V X *R 4 /(R 3 +R 4 ).įor the PSRR specification the applicable formula is: From the VX value you can calculate the offset voltage (V OS ). In this circuit, V OS is extracted at the VX node. Finally, A OL is measured by observing V OS changes as V OUT changes.įigure 2 shows a simple circuit diagram that you can use when measuring these specifications at DC. The amplifier CMRR is measured by observing how the voltage offset changes as the input common-mode voltage at the amplifier’s input stage changes. You can measure the PSRR by changing the power supply voltages and how the voltage offset changes. Its level may shift the results of some of the amplifier’s other important parameters: the power-supply-rejection-ratio (PSRR), the amplifier’s common-mode-rejection-ratio (CMRR), and the open-loop-gain (A OL ) specifications. īut, the consequence of this error goes much deeper than simply an output offset voltage. Figure 2 Amplifier application circuit to measure DC V OS, PSRR, CMRR, and A OL.
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