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simple circuit to provide dc shift?

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Mvar

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Hi,

This is just a question about design using LTSpice using only LV MOSFET's.
Supposed I have a signal between (1.2v-3.7v), I need this to be in the range of (0v-3.3v), so a DC shift of 0.4v down would do the trick. Would this be possible with just MOSFET's and a power supply of (0v-3.3v)?

1. Is this possible at all?
2. A simple circuit that can provide a DC shift using the W/L of MOSFET's maybe?

thanks
 

KlausST

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Hi,

It depends what accuracy you need.

A diode in series with a risistor could do the job
Or a two resistor voltage divider.

Klaus
 

SunnySkyguy

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What is the load? Only 1 signal? What rate?



Most 3V logic uses and input threshold of 1.25V with margin expected to be 0.8 to 1.7 for inputs to swing past these levels for good noise margin.


But 74HC family uses Vcc/2 thresholds and operate down to 3V, so you can use either family and use a series R and the R shunt to ground to shift the level with at least 0.6V swing centred around input threshold.



It seems you have 2.5V swing so plan on a 2V swing centred around 1.25V using 2R's chosen for thus using values in the 10k range, unless you have other constraints.

I"ll let you calc the values.


Do not exceed the CMOS supply rail , as the clamp diode current has an input limit = 10mA.typ.
 

schmitt trigger

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Most likely the OP's question was a coursework assignment or question.
He may have already found the answer somewhere else.
 

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