Help me measure distance using an analog circuit

Hey.
I need to measure a distance (it should be no more than 50cm) using an analogic circuit.

can someone help me?

The usual way is to modulate an IR beam with a sine wave and compare the phase of the modulation between transmitting and receiving.

Another way is from triangulation. The IR sender and receiver are spaced on a baseline and the transmitter and receiver can be turned in angle. They are done so that the reflected beam is picked up by the receiver.

you can also use ultrasonic transmitter and receiver.
send 3-5 pulse and measure time between send and receive.

don't you have any schematic circuit for me to be based on?

thanks