convert 0 to -1 volts into 0.5 to -0.5 volts using opamp

[vanashree]

i want to convert 0 to -1 volts into 0.5 to -0.5 volts using opamp. i dont want to boost the voltage. i just want level shift it.kindly help as soon as possible

 

[FvM]

You can refer to a single OP differential amplifier https://en.wikipedia.org/wiki/Differential_amplifier#Other_differential_amplifiers
A reference voltage is needed for the level shift. Depending on the available reference, the resistors have to be adjusted.

 

[FANT]

Get an OP-Amp ( and supply it from -5 to + 5 volt ).
connect your source 0-1 volt to a 10 KOhm resistor; the second terminal of the resitor to the + input of the Op-Amp.
Connect a second resistor 10 KOhm from + input to GND.
connect a third 10 KOhm resistor from output to - input.
A fourth resistor of 10 KOhm from - input to a + 0,5 volt.

Of course, the less tolerance the resistors are, better is the conversion precision.

You can change the resistors value ( all must be the same ) from 1 K to 1 M without problems depending availability and your needs ( i.e input impedance)
The +0,5 V must be a low resistance source.

Mandi

 

[FvM]

A fourth resistor of 10 KOhm from - input to a + 0,5 volt.

To achieve the intended transfer function with a G=1 differential amplifier, a - 0,5 volt reference is needed.

A positive reference could be e.g. summed into the non-inverting amplifier input.

 

[Analog Ground]

A great type of part for this kind of application is a "difference amplifier" such as the INA105 from TI. Four tightly matched resistors are combined with an op amp in a single package. Analog Devices and TI make lots of these types of parts with different bandwidths, power and accuracy. Combine one of these with a low output impedance, 0.5 volt reference source and your done. This will give you an extremely accurate solution with a low parts count. Put a -0.5V reference on the inverting input and the signal to be shifted on the non-inverting input with the other non-inverting input to ground and your done. Or, put a +0.5V reference on the other non-inverting input and ground the inverting input. Now, for the reference voltage.... Another post? Checkout the TI and Analog Devices data sheets for these parts for circuit examples which will do exactly what you need. If your design is for a class assignment, check these out anyway. They solve your problem. For example, Figure 15 on the INA105 data sheet shows the circuit with a positive reference.

The posts above have the right idea but do not always get the sign of the level shift and signal amplification correct.

 

[BradtheRad]

The job can be done by a positive voltage source and potentiometer... if you tolerate some reduction of signal.

- - - Updated - - -

General op amp method.

If your power supply is regulated, then a potentiometer can be used to draw a portion of it and add to your incoming signal.

The op amp provides gain to restore 1V swing to your signal.