question about voltage comparison

[danda821]

Hello,

I need to design a circuit to compare two voltages. One is high (1V), the other is low (0.1V). Whenever there is a voltage ratio increase or drop between high voltage and low voltage (nominal value is 10), a flag need to be generated. Any simple circuit to do this kind of non-1:1 comparison.

Thanks.

danda821

 

[chuckey]

use an opamp, feed the 1V into a 10 :1 divider, say a 100K in series then a 10K to earth, the junction take to the positive input. Feed the .1V into the negative input. The output will be negative if the .1 V is more then .1 X the one volt input. i.e. -.15, 1 v O/P = - Vcc or .1 V input = .07V, O/P = + Vcc
Frank

 

[danda821]

Thanks for the reply. Forgot to mention all signals are differential. 1V: one side is 0.2V, the other side is 1.2V. 0.1V: one side is 0.65V, the other side is 0.75V. I do not want to draw any current from existing circuit, so voltage divider is not preferred.

use an opamp, feed the 1V into a 10 :1 divider, say a 100K in series then a 10K to earth, the junction take to the positive input. Feed the .1V into the negative input. The output will be negative if the .1 V is more then .1 X the one volt input. i.e. -.15, 1 v O/P = - Vcc or .1 V input = .07V, O/P = + Vcc
Frank