rubber diode

File:PP stage Vbe multiplier.png

In electronics, a rubber diode or V{{sub|BE}} multiplier is a bipolar junction transistor circuit that serves as a voltage reference. It consists of one transistor and two resistors, and the reference voltage across the circuit is determined by the selected resistor values and the base-to-emitter voltage (V{{sub|BE}}) of the transistor. The circuit behaves as a voltage divider, but with the voltage across the base-emitter resistor determined by the forward base-emitter junction voltage.

It is commonly used in the biasing of push-pull output stages of amplifiers, where one benefit is thermal compensation: The temperature-dependent variations in the multiplier's V{{sub|BE}}, approximately -2.2 mV/°C, can be made to match variations occurring in the V{{sub|BE}} of the power transistors by mounting to the same heat sink.{{cite book |last1=Crecraft |first1=David |last2=Gergely |first2=Stephen |date=May 21, 2002 |title=Analog Electronics |url=https://books.google.com/books?id=lS7qN6iHyBYC&dq=vbe+multiplier&pg=PA188 |publisher=Butterworth-Heinemann |page=188 |isbn=0080475833 |access-date=August 11, 2015 }} In this context, it is sometimes called a bias servo.{{cite web |url=https://sound-au.com/amp_design.htm |title= Power Amplifier Design Guidelines |last= Elliott |first= Rod |date= 27 Dec 2006 |website= Elliott Sound Products |access-date= Oct 1, 2021}}