Level shifter comparator circuit with hysteresis

117

01:04:00

Can be used from shifting 2V input to 5V output, 5V input to 2V output, and anything in between. 

Hysteresis is about 5% of Vout; for a 5V output, this means approximately 250mV hysteresis.  If not convinced, use superposition: dVin-/dVout= (100k//100k)/[100k//100k+1M]=50k/1.05M=4.76%.

That hysteresis keeps the circuit from double pulsing for slow or non-monotonic edges on the input; this is critical for fast digital circuits.  It is also nice to have an output logic level that can be completely independent from the input logic level.

published 3 years ago

mapplejacks

3 years ago

Additional note: the voltage divider to Vin- should be from the logic supply rail of your input logic to give a mid-rail threshold. Also notice how the Vin+ slow edge becomes faster and sharper on the output; this is a feature.

592azy2circuitdude

3 years ago

Am I correct that the opamp has negative feedback? I thought that positive feedback is required to create hysteresis (like a Schmitt Trigger). Also, would you please explain what the MOSFETs on the left are for? Thanks.

592azy2circuitdude

3 years ago

Excuse me, the MOSFETs on the right.

mapplejacks

3 years ago

@592azy2circuitdude you're absolutely right. I've uploaded a revised version. I missed while eyeballing the datasheet that the resistor went to OUTB and not OUT. The CMOS inverters are just there to demonstrate the new logic level

592azy2circuitdude

3 years ago

Swell. 👍

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