Uses of ICs outputing 1 value only
You can only understand such circuits if you know the inner schematic of the inverter block used. It uses the inverter as a comparator and inverting amplifier.

For example, if this was a single-stage CMOS inverter (as found e.g. in the CD4007 chip), the resulting circuit would be as follows:







simulate this circuit &ndash; Schematic created using CircuitLab

The diode renders the lower MOSFET ineffective. It cannot pull the output to ground any more. But the upper MOSFET can still connect Vdd to the output, if the input is below 0.5·Vdd (this is a characteristic of CMOS inverters). So, the function is as follows:


input below 0.5·Vdd: output at Vdd with high-current capacity
input above 0.5·Vdd: output at input voltage with low current capacity (through the resistor)


The resistor must be large enough so the input can be easily driven low by the feeding circuit to the left. If it isn't, this circuit will oscillate at a few MHz.

This circuit may be used for a pullup of variable strength, for example.