The ES11 consists of three independent functions which are useful in the production of square waves and variable pulse waves.
The comparator reference level can be a time-varying control voltage, a complex audio signal, or a fixed preset voltage. Additionally, the comparators are useful for level detection and for logic decisions based on amplitude.
The comparator has basically 3 functions:
- as a pulse width modulator
as a logic comparator
1) Pulse Width Modulator; Patch a sawtooth wave into the [-/PWM] input. With the [PWM CMP] knob fully to the left you will get a square wave output with a 50% duty cycle. Turning the pot to the right will reduce the duty-cycle until when you get to the diagonal line at 11 o'clock when the duty cycle will be approximately 8%. Turning the knob passed this line will have no effect (in reality the duty cycle will drop to about 3% over the remainder of the range). In this mode, the [+/CMP] input can be used as a control voltage input into the pulse width modulator. When this is done, the pot will act as a sort of processor.
2) Squarer: Patch a constant frequency pulse or sawtooth into the [-/PWM] input. Turn the knob fully to the left. The output will be a square wave.
3) Comparator: Patch a sawtooth into the [+/ CMP] input with the [PWM CMP] knob fully to the right. The result will be a pulsed output with a duty cycle of ~15% . As the knob is turned towards '1', the pulse ON time increase and at about '2' a square wave with a 50% duty cycle will be generated. Turning further to '1' will increase the pulse ON time to about 88% and then at '0', the output will go HIGH (100%) and remain there, as now the positive input of the comparator will always be higher than the negative input.
The module also contains a single, non-adjustable, Schmitt Trigger. This is a single-input comparator with hysteresis. Hysteresis means that the switching thresholds are different for an input signal depending upon whether it is going up or down. This feature can be used with an envelope and VCA functioning as a noise gate to reject low-level background noise in audio applications.
The Schmitt trigger [OUTPUT] will rise to ~5 volts when the input falls below ~0.6 volts and will fall to ~0 volts when the [INPUT] rises over ~4.3 volts.