I would like to know if you get your expected results. 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. Connect a potentiometer to the balance pins as shown in Figure 2.3(b). Before you wire your integrator, temporarily short the input pins of the OA together (it may be a good idea to short them both to 0V). 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. Use the offset null or balance pins provided by most OAs (e.g., OAs shown in Figure A.1). 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. 39 The output dc offset voltage of an op amp can be trimmed to zero by connecting a potentiometer to the two offset-nulling terminals. Answer: It is the voltage that appears at the output terminal of an Op-amp when both the input terminals are grounded(no inputs are applied). The transfer function of an ideal Op Amp is described by the equation y A ( V.
In this article, a generalized method is proposed to compute offset in the output when an Op Amp with an input offset e is used in the circuit.
Figure 2 Amplifier application circuit to measure DC V OS, PSRR, CMRR, and A OL. Electronics System Design Introduction Hafiz Malik Op Amp: Offset Voltage Nulling Some op amps provide with additional terminals to connect a specific circuit (e.g. The presence of offset voltage is a well-understood phenomenon and is described in various literature and textbooks.