[quote userid="354815" url="~/cadence_technology_forums/f/custom-ic-design/37202/ahdllib-opamp-model-vref-pin/1355641#1355641"]However, it is strange that output common mode voltage doesn't change when I vary the vref.[/quote] It's not strange at all. The opamp DC output voltage is defined by your feedback circuitry. Given that the two input pins must be (almost) equal (because of the high gain), and the dc level of the sinusoidal source is 0V, the voltage across both R0 and R1 will be 0V too. If there had been a dc component in the sine source, the voltage across R0 would end being the same as that DC component, and so the DC level of the output voltage would be 10 times higher (plus the 1V from V5). For example, if you set dc on Vin1 to 0.05 then the DC level at the output of the amplifier would be 0.5*10+1=1.5V. That's how opamps work. The Vref is just used in the output stage; it does not set the DC level of the output of the amplifier otherwise it would not operate correctly as an opamp. Regards, Andrew.
↧