How to determine divider resistor as the input to ADC?

shteo83 · Mar 1, 2006

I going to do a digital oscilloscope project. But my ADC is only -0.6v to +2.6V analog input range. I need a voltage id from negative voltage to positive voltage. In my case suppose to get
-2.6v to +2.6. How to the divider resistor? what should be the resistor value? My ref is 2.6v.

akg · Mar 1, 2006

shteo83 said:
I going to do a digital oscilloscope project. But my ADC is only -0.6v to +2.6V analog input range. I need a voltage id from negative voltage to positive voltage. In my case suppose to get
-2.6v to +2.6. How to the divider resistor? what should be the resistor value? My ref is 2.6v.

the -0.6 and 2.6v comes from the input clamping diodes? , then the recommended is 0-2v for FSD. u need a voltage divider , the measuring range will decide the resistor vals. if u need to measure -ve volts,add a level shifter/dc offset.

ljcox · Mar 2, 2006

The ADC that I am familiar with has an input range of +0.6 to +2.6V so are you sure about the -0.6V ?

If you want the range to be -2.6 to +2.6V then you need to shift the level and attenuate the signal.

This could be done with 3 resistors. Use McMillman's Theorm to calculated the voltages.

shteo83 · Mar 6, 2006

My adc is TLC5540INS. It has two option, one is from -0.6 to 2.6 and one is from 0 to 2.28V. Now i care about the 0-2.28v. So how to make it
-2.28vto+2.28?

Nigel Goodwin · Mar 6, 2006

shteo83 said:
My adc is TLC5540INS. It has two option, one is from -0.6 to 2.6 and one is from 0 to 2.28V. Now i care about the 0-2.28v. So how to make it
-2.28vto+2.28?

Feed it from an opamp, setting it's gain and offset to provide the range you need.

ljcox · Mar 6, 2006

In fact, all you need are 2 equal resistors. Their value will depend upon what frequency response you want.

Vin -------R1-------- to ADC input

Then connect R2 from the ADC input to a 2.28 Volt source.

When Vin = -2.28, Vout = 0, and when Vin = +2.28, Vout = 2.28.

R1 = R2

However, you may need an Op Amp configured as a unity gain buffer before R1.

How to determine divider resistor as the input to ADC?

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