US 2002/0053928 A1Published application

Precision, low-power transimpedance circuit with differential current sense inputs and single ended voltage output

AssigneeIntersil Corporation

InventorLeonel Ernesto Enriquez

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Abstract

A transimpedance circuit adapted for use in a subscriber line interface circuit includes sense resistors installed in closed loop, negative feedback paths of respective sense amplifiers. Voltage drops across the sense resistors are applied to first and second differential coupling circuits for applying differential currents to complementary polarity inputs of an operational amplifier. The inputs of the amplifier are also coupled to a linearity compensator, that is configured to provide sufficient overhead voltages in the presence of worst case voltage swing conditions. The compensator has a differential amplifier configuration, that closes a negative feedback loop from the output of the amplifier and one of its inputs, relative to a reference voltage balancing path coupled to the amplifier's other (complementary) input. The balanced differential configuration forces corresponding terminals of a pair of load resistors coupled to the inputs of the operational amplifier to the same potential, irrespective of variations in the input currents.

Claims20

Dependent claims

A transimpedance circuit comprising:

an operational amplifier having first and second complementary polarity inputs and an output;
a first sense resistor coupled in a first current sense path;
a first differential coupling circuit coupled between said first sense resistor and said first and second complementary polarity inputs of said operational amplifier, and being operative to apply a first differential input current to said first and second complementary polarity inputs of said operational amplifier in accordance with a first voltage across said first sense resistor;
a second sense resistor coupled in a second current sense path;
a second differential coupling circuit coupled between said second sense resistor and said first and second complementary polarity inputs of said operational amplifier, and being operative to apply a second differential input current to said first and second complementary polarity inputs of said operational amplifier in accordance with a second voltage across said second sense resistor;
and
a compensator circuit coupled between a supply voltage node and said first and second complementary polarity inputs of said operational amplifier, and being operative to close a negative feedback path from said output of said operational amplifier to said first input of said operational amplifier, relative to a voltage balancing path coupled to said second input of said operational amplifier, and equalize voltages applied thereby to said first and second complementary polarity inputs of said operational amplifier, irrespective of variations in currents through said first and sense resistors.

4 more elements

A transimpedance circuit for converting a differential input current through first and second current paths into a single ended output voltage, while rejecting common mode currents through said first and second current paths comprising:

a first current sensing element coupled with said first current path;
a second current sensing element coupled with said second current path;
an operational amplifier having first and second complementary polarity inputs and an output from which said single ended output voltage is derived;
a first differential coupling circuit operative to couple a first differential input current to said first and second complementary polarity inputs of said operational amplifier in proportion to a first current flowing through said first current path;
a second differential coupling circuit operative to couple a second differential input current to said first and second complementary polarity inputs of said operational amplifier in proportion to a second current flowing through said second current path;
and
a compensator circuit coupled between a supply voltage node and said first and second complementary polarity inputs of said operational amplifier, and being operative to equalize voltages applied to said first and second complementary polarity inputs of said operational amplifier, in accordance with a prescribed relationship between said single ended output voltage and a reference voltage.

4 more elements

A method for converting a differential input current flowing through first and second current paths into a single ended output voltage, while rejecting common mode currents through said first and second current paths comprising:

(a) coupling first and second current sensing elements with said first and second current paths, respectively;
(b) coupling a first differential input current to first and second complementary polarity inputs of an operational amplifier in proportion to a first current flowing through said first current path, and coupling a second differential input current to said first and second complementary polarity inputs of said operational amplifier in proportion to a second current flowing through said second current path;
and
(c) equalizing first and second equalized voltages coupled to said first and second complementary polarity inputs of said operational amplifier, in accordance with a prescribed relationship between a single ended output voltage derived from an output of said operational amplifier and a reference voltage.

1 more element

Dependencies are inferred from the claim text.

Facts

Application: 09/939,191Filed 24 Aug 2001
Priority: 11 Oct 2000
Published: 9 May 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

H03F 3/45085
Using bipolar transistors as the active amplifying circuit: long tailed pairs
H03F 2203/45392
Indexing scheme relating to differential amplifiers: the AAC comprising resistors in the source circuit of the AAC before the common source coupling
H03F 2203/45574
Indexing scheme relating to differential amplifiers: the IC comprising four or more input leads connected to four or more AAC-transistors
H03F 2203/45604
Indexing scheme relating to differential amplifiers: the IC comprising a input shunting resistor

Family

Application09/686,506Continuation · filed 11 Oct 2000
Application09/939,191Continuation · filed 24 Aug 2001
US 6,292,033 B1Related patent
US 6,400,187 B1Related patent
US 2002/0053928 A1This patent

From the US filing history. Foreign family members aren’t listed.