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OPA4197: possible SPICE model issue

Part Number: OPA4197

This is a rail to rail input device.   I'm simulating it with a single supply and common mode voltage at the negative rail.  The device is specified for this operation and has a Vos spec of 100 uV max, 25 uV typical.   The sim is  returning a Vos of approx 2 mV.   If I inject a few mV of DC offset into the input signal and thus raise Vcm a bit off the negative rail, Vos then is then at the 25 uV typ value.  Is this the actual behavior of the device or is it an artifact in the SPICE model?

thanks much,

Martin Rockwell

  • Martin,

    Yes, OPA4197 has rail-to-rail input common-mode voltage - actually, it can go 100mV beyond the rails.  However, you most likely simulate the circuit on single supply in a buffer configuration and thus what limits the voltage swing is the output and NOT input - unloaded output can swing only within 5mV of either rail - see below.