A concept which I’ve been pondering is, that a circuit could be designed which requires a controlled voltage, negative by a stable amount from the supply voltage, yet, where the supply voltage may only be 3V. And one of the assumptions I’m making is that, once a certain number of pins on the IC have been allocated to external, discrete components, additional discrete components can be connected to the same pins, at little additional cost.
Having said that, the fact is already established in circuit design, that the supply voltage itself is a big source of errors. It could take the form of a battery-set that goes weak, or a power-supply, the output of which is fettered by unpredictable behaviours from the circuitry which it is providing the supply voltage to. And such unpredictable behaviours could include low-frequency phenomena such as widely varying current drawn, so that simply to connect a power-supply capacitor will not remedy this issue.
Thankfully, 2.4V Zener diodes are now a part of what can be mass-produced. What this means is, that the Zener diode can be connected to the supply voltage at one end, thereby not taking up any pins on the IC, but connected to one pin of the IC at the other end, which is to be at -2.4V with respect to the supply voltage. That pin of the IC could serve two purposes:
- To provide an internal, series-connected resistor, to keep the Zener diode operating within its assigned current-range,
- To provide whatever reference voltage the IC itself might require, that would be (Vcc-2.4V).
But ultimately, the point was not, that an exact (Vcc-2.4V) be made available. The point was that a Control Voltage of (Vcc-X) be made available, where (X) is supposed to remain accurate. And so, to accomplish that, a 200kΩ Trimming Potentiometer can be connected in parallel with this Zener diode, again not taking up any pins of the IC. But, the wiper of this potentiometer can in fact be connected to one additional pin of the IC, where a calibrated voltage (Vcc-X) becomes stable. This can be repeated, only taking up one additional pin of the IC each time.