I need a little help with designing a circuit.

[ckramer]

Hey I need a little help with designing/drawing a circuit. Can someone make me a sketch or help me with the solution?

Here is the my problem:
I’m going to make a measurement system for a bridge (AC bridge circuit). The measure-elements in the bridge can be resistive, for example: a Pt-100-element for measuring temperature, or a strain gauge for measuring pressure or power, or it can capacitive so that it can measure air humidity.
The bridge is going to be driven by AC, and shall be square-, triangle-, or sinus-shaped. The frequency on the AC shall be in the area from 400Hz – 1kHz. The reason for using AC is because we can reduce influence of the amplifiers DC-error.
When the bridge is driven by AC-voltage, then of course the bridge’s output signal will be AC. And this output signal must be demodulated. And the method I supposed use, is with Phase Sensitive Detection.


Task:

[ckramer]

And btw. I've made the square wave amp, the bridge and the instrumentation amp. But I'm a little unsure how to design the phase shift circuit and the demodulator.