Reciprocal amplifier - uout = C/Uin

Many readers may judge that the subheading is rather simple. Just take a calculator and choose a number, then press the 1/X key and the result will be displayed instantly. However, to "treat" a d.c. voltage this way, in order to use its reciprocal value in a measuring circuit, is something else entirely! The normal circuit design for a re- ciprocal amplifier uses four ICs. Two opamps, ICs 2 and 4, serve as input buffer and output driver respectively. Half of a dual timer IC3a forms a clock oscillator for a modulator, IC3b (the other timer). Gates N1 and N2 convert the output signal of IC3b into a "pure" square wave signal. This cir- cuit is -based on the PPM (pulse pause modulation) principle and the variable pulsewidth of the square wave signal is dependent on the DC voltage level fed to the modulator. Note, the frequency remains unchanged! For example, if the input to the circuit is a high voltage level, the pulse width of the square wave signal will be small. The output of IC...