A diode is inserted in the op amp's negative feedback path in order to exploit the virtual short effect when the diode is ON. When the diode is OFF, however, the op amp's feedback loop is broken and the op amp is forced to its rail. In this circuit, the output signal is taken from the op amp's inverting input; the op amp's output terminal is used to bias the diode. Note that this simulator doesn't show the effect of slew rate limiting.
