//Please switch on at the right top corner - it won't start if voltage source is already connected.//
I'd like to present you the circuit based on old (soviet) integral circuit К525ПС1 (K525PS1). This IC is actually an analog multiplier. I reproduced its internal structure taking up left two-thirds of the diagram "as it is" but for almost each of the connection types of this IC some(quite a lot) external components are also needed for its correct operating. So i was forced to eliminate some (important) external parts due to running out of workspace and this simplification (replacing of the balancing bridge just by connection some terminals to the ground) actually led to the significant loss of precision of multiplication. I'll try to correct this little flaw in future. Transistors, diodes and resistors at the lower part of the diagram play a role of constant current sources so they certainly can be replaced for appropriate equivalents. At first stage i just want to show how this circuit looks like and how it approximately works. Blue plot is the output signal which in fact roughly equals to (U1(green)*U2(orange))/10. The scaling coefficient (1/10) is usual thing for such kind of circuits because of the product value U1*U2 where U1, U2 expressed in volts exceeds source voltage for some set of pairs (U1, U2) (without mentioned scaling) that in general we do not want to loose as a suitable pairs of input signals.
// See also MC1495 and MC1495L - four quadrant multipliers
