Sine to Square Wave

This circuit is intended to provide good square waves converting a sine wave picked-up from an existing generator. Its main feature consists in the fact that no power-source is needed: thus it can be simply connected between a sine wave generator and the device under test.

This circuit was designed to convert a low amplitude 40KHz signal into a clean square wave signal. It will work with inputs as small as 5mv peak-to-peak or as large as 3 volts peak to peak. The input frequency can range from a few kilohertz to about 150KHz.

Figure 1 shows the typical output from a spectroscopic amplifier, where the presence of a large amount of detector noise with Gaussian distribution is a limiting factor for system performance in amplitude and timing resolution. The time-tagging of such pulses is subject to two well-known types of errors: the jitter related to the noise and the "walking time" arising from the amplitude variation of the signals.

Generating a true sinewave from an input square wave over an octave in frequency is not simple. A sinewave oscillator would be easy. Filtering to the fundimental would be easy for a frequency range less than an octive. The best I was able to come up with is the attached circuit which approximately generates the sine of the input voltage. Integrating the squarewave to a triangle wave and inputting it to the circuit below should work.

This circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit. The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit.

Current-feedback amplifiers have wide bandwidths and relatively small and constant propagation delays. These small, constant delays help meet the setup-and-hold requirements of digital logic. Typically, current-feedback amplifiers have delays from 1.1 to 5 nsec.

This Circuit is a zero crossing detector, which produces an output state change whenever the input crosses the reference input. In this case the reference input is connected to ground. The output of the comparator can easily drive multiple outputs, which can include, for example, a relay, acontrol gate and a LED indicator.