4412347 Precision Setting of Currents and Reference Voltages Aug81

This patent describes a precision voltage and current source, primarily designed for transceivers in carrier-sense multiple access/collision detection (CSMA/CD) communication networks. Its main purpose is to generate highly accurate threshold voltages required to differentiate between the absence of a signal, a single signal on the network, and a collision (multiple signals).

The system operates by:

1. Generating Thresholds: A current source pulls current through a precise resistive load to produce the required threshold voltages. This load is typically two resistors in series, creating two distinct thresholds: one for normal signal reception and one for collision detection.
2. Regulation Mechanism: A feedback loop is established where a voltage proportional to the current source's output current (and thus the threshold voltage) is compared against a stable reference voltage derived from a Zener diode.
3. Error Correction: Any difference (error) between the feedback voltage and the Zener reference controls a shunt regulator, which, in turn, adjusts the main regulated power supply voltage. This adjustment ensures the voltage across the precision resistive load consistently matches the Zener reference, thereby maintaining precise threshold settings.

A key innovation is the efficient use of a single Zener diode to regulate two different parts of the power supply system (e.g., a main -10.2V supply and a -5.2V supply for the current source) through distinct feedback mechanisms, ensuring overall stability and accuracy for the critical threshold voltages.