A design problem regarding voltage generator

[jiesteve]

Let's say I have a voltage generator that generates a voltage called V1. I want to produce an output, Vout where Vout = V1 + V2.

I want V2 to be some sort of voltage DAC, that is process and temperature independent. Could you please give some circuit solutions, and the pros/cons of each?

Thanks!

 

[jecyhale]

Re: A design problem

I think you can add the current. Vout=(I1+I2)*Ro
And the current can be generated by the limiter.
So I1=V1/R1, I2=V2/R2.
Then you should match R1, R2 and Ro.
That will be ok.

 

[Fom]

A design problem

If to take two voltage source and connect them with two equal series resistors the middle point of the resistor will have voltage V=(V1+V2)/2

 

[present]

Re: A design problem

You will need a opamp and make a circuit like this.
Let R1=R2=R3, then Vo=-(V1+V2).

 

[jiesteve]

Re: A design problem

You will need a opamp and make a circuit like this.
Let R1=R2=R3, then Vo=-(V1+V2).

Thanks. Could you please show how I can make a PVT independent voltage DAC to generate V2? Also, how can I make Vo positive (remove the negative sign) ?

Thanks

 

[leo_o2]

A design problem

It can be generated based on bandgap voltage.

 

[present]

Re: A design problem

You can use a bandgap circuit to get a PVT independent voltage.
You can use a basic inverting opamp configuration to get Vout=-Vin.

Ps, DAC means digital to analog conversion, but r u using this?

Thanks. Could you please show how I can make a PVT independent voltage DAC to generate V2? Also, how can I make Vo positive (remove the negative sign) ?

Thanks

 

[jiesteve]

Re: A design problem

The circuit above requires a negative rail. I only have VSS=0... How do I get around that? Wouldn't the op-amp just rail to 0 ?

 

[elantra]

A design problem

the rail is relative, in other words, you can connect the input of the opamp to 0.5 Vcc, then it's OK to assume that the opamp uses "negative rail" of 0.