# Level shifter with variable DC level shift

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#### marzie

##### Newbie level 2
Hi,

I am looking for a level shift which shifts an analog circuit with a variable ( tunable) DC level.
means for example I can change the analog voltage with 15volt once, and next time may be -10. the range of change for the DC is (-20 to 20).

Another solution could be adder; to add the analog voltage to the tunable DC voltage.

any suggested circuit?

#### RF_Jim

##### Full Member level 3
Do you have a frequency range in mind?

Like just audio range (20 - 20,000 Hz) or video frequency range (20 Hz - 6 MHz) or DC/Low freq AC for instrumentation (DC Hz - 400 Hz)?

Simple op-amp circuits can provide 'shift' function, although +-20 volts starts to get difficult to do if you really need a wide frequency range.

Jim

#### marzie

##### Newbie level 2
the voltage is the baising voltage of an Avalanceh phorodiode and the freq is depend on the photon coming to photodiode.

maybe my question is so basic but can u show me one simple op-amp circuit which can do this function?

Do you have a frequency range in mind?

Like just audio range (20 - 20,000 Hz) or video frequency range (20 Hz - 6 MHz) or DC/Low freq AC for instrumentation (DC Hz - 400 Hz)?

Simple op-amp circuits can provide 'shift' function, although +-20 volts starts to get difficult to do if you really need a wide frequency range.

Jim

#### RF_Jim

##### Full Member level 3
the voltage is the baising voltage of an Avalanceh phorodiode and the freq is depend on the photon coming to photodiode.

maybe my question is so basic but can u show me one simple op-amp circuit which can do this function?

marzie,

Here is a good place to start, about 1/2 way down the page is the basic theory (and maths) and simple circuit (showing a generic op-amp) showing a +-1 V signal transposed to 0 to 2 VDC (for, say, feeding to a ADC which only has a 0V to 2V input range):

Op Amp Summing Amplifier

Of course, your specific application will need to know actual voltage levels to be shifted to, and your frequency response is probably not actually the 'speed of light' but rather some more reasonable rate-of-change like several kilo Hertz to perhaps a couple MegaHerz depending on the source creating the light energy (how rapidly it turns on and off, rather than the fact it is 'light' energy as a photodetector diode provides an output voltage proportional light amplitude, and the output will roughly 'follow' the enevelope of the light that is shined on it).

Hope this is of some help.

Jim

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