US 6,191,635 B1Granted

Level shifting circuit having a fixed output common mode level

AssigneeTelefonaktiebolaget LM Ericsson

InventorsJohn Thompson, Raymond Filippi

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Abstract

The invention relates to an electronic circuit, and in particular embodiments to a level shifting circuit having an output common mode voltage independent of the input common mode voltage, and unity differential signal gain. The circuit receives first and second input voltages, referenced to a first voltage supply rail, and has first and second resistors, each connected to the first input terminal, and third and fourth resistors, each connected to the second input terminal, the second and third resistors having equal resistance values. The first resistor is also connected to a first output terminal, the fourth resistor is also connected to a second output terminal, and the second and third resistors are also connected together at a reference node. A first current source draws a current through the first resistor, a second current source draws a current through the fourth resistor, and a third current source draws a current through the second and third resistors and the reference node, and sets a reference voltage, referenced to the second voltage supply rail, at the reference node. The first and fourth resistors, and the first and third current sources, are such that the voltage drops across the first and fourth resistors are equal.

Claims8

Dependent claims

A level shift circuit, having first and second voltage supply rails, the circuit comprising:

(a) a first input terminal, connected to receive a first input voltage, referenced to the first voltage supply rail;
(b) a second input terminal, connected to receive a second input voltage, referenced to the first voltage supply rail;
(c) first and second resistors, each having respective first and second terminals, each of the first terminals being connected to the first input terminal;
(d) third and fourth resistors, each having respective first and second terminals, each of the first terminals being connected to the second input terminal,
the second and third resistors having equal resistance values,
the second terminal of the first resistor being connected to a-first output terminal,
the second terminal of the fourth resistor being connected to a second output terminal, and
respective second terminals of the second and third resistors being connected together at a reference node;
(e) a first current source, connected to draw a current through the first resistor;
(f) a second current source, connected to draw a current through the fourth resistor;
and
(g) a third current source, connected to draw a current through the second and third resistors and the reference node, and setting a reference voltage, referenced to the second voltage supply rail, at the reference node;
wherein the first and fourth resistors, and the first and third current sources, are such that the voltage drops across the first and fourth resistors are equal.

10 more elements

Dependencies are inferred from the claim text.