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Reference Voltage Generator for Constant Current Source

IP.com Disclosure Number: IPCOM000036703D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Diemoz, TE: AUTHOR [+3]

Abstract

Regulated reference generators are essential for emitter-coupled logic (ECL) and common-mode-type logic families. The reference voltage Vx is used to supply a regulated potential across a resistor to create a constant current source for a logic gate, as shown in Fig. 1. The current i is given by: i = (Vx-Vbe-Vee)/Re

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Reference Voltage Generator for Constant Current Source

Regulated reference generators are essential for emitter-coupled logic (ECL) and common-mode-type logic families. The reference voltage Vx is used to supply a regulated potential across a resistor to create a constant current source for a logic gate, as shown in Fig. 1. The current i is given by: i = (Vx-Vbe- Vee)/Re

In order to maintain a constant current, the difference between Vx and Vee must be kept constant and independent of other circuit environment parameters. The circuit shown in Fig. 2 is a generator circuit that meets those requirements and is the subject of this article.

Referring to Fig. 2, transistors T1 and T2 are connected as diodes, with series resistor R1 controlling the current in the diodes. Assuming the value of R1 to be large, there will be only minor diode current changes when the (Vcc-Vee) differential voltage changes. Therefore, the voltage at the base of T4 will be 2Vbe above Vee, and relatively independent of Vcc. As a result, T4 acts as a constant current source of value Vbe/R2. This current flows through PNP transistor T3. Since PNP transistors T3 and T5 have their bases and emitters connected together, i.e., current mirror, the same value of current will flow through the collector of transistor T5. This current i2 flows through a Vbe multiplier, built with transistor T6 and resistors R3 and R4, as well as the diode made up of transistor T7, to generate the desired voltage differ...