High gain, low offset input amplifier

• US 5,699,012 A
• Filed: 02/28/1996
• Issued: 12/16/1997
• Est. Priority Date: 02/28/1996
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hakkarainen, Juka Mikko
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US08/608,394
• Time in Patent Office: 657 Days
• Field of Search: 330/9, 330/69, 330/252, 330/260, 330/261
• US Class Current: 330/9
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/45479 characterised by the way of common mode signal rejection

Abstract

An input signal buffer amplifier that has a high gain and a low offset voltage is implemented as an integrated circuit (IC) along with other components that perform further processing on an input signal. In one embodiment, the buffer amplifier includes first and second operational amplifiers (op amps). Voltage divider resistors R1 and R2 are connected in series between a positive voltage supply rail and a ground rail of the IC. The positive input terminal of the second op amp is electrically connected to a node between resistors R1 and R2. A feedback loop is established from the output of the second op amp to its negative terminal. The negative terminal of the first op amp is connected to a node between a series-connected input resistor and feedback resistor. The positive input terminal of the first op amp is connected to a node between series-connected voltage divider resistors R3 and R4 which are connected across the output of the second op amp and the ground rail. The first operational amplifier generates an output voltage signal VI+ and the second operational amplifier generates an output voltage signal VI-.

Claims

1. An input signal amplifier comprising:

a first operational amplifier;

a biasing amplifier comprising a second operational amplifier;

first and second voltage divider resistors coupled in series for connection across a DC bias voltage, a first input terminal of said second operational amplifier coupled to a first node between said first and second voltage divider resistors;

a feedback loop coupling an output of said second operational amplifier to a second input terminal of said second operational amplifier;

third and fourth voltage divider resistors coupled in series, said third resistor being coupled to said output of said second operational amplifier, a first input terminal of said first operational amplifier coupled to a second node between said third and fourth voltage divider resistors for receiving a fixed bias voltage; and

a second input terminal of said first operational amplifier coupled to receive an input signal and, in response thereto, to generate an output signal Vout.

2. The input signal amplifier recited in claim 1 including a feedback resistor coupling an output of said first operational amplifier to the second input terminal of said first operational amplifier.

3. The input signal amplifier recited in claim 2 including an input resistor coupled to the second input terminal of said first operational amplifier.

4. The input signal amplifier recited in claim 3 wherein:

##EQU7## where V_X1 is a voltage signal applied to the first input terminal of said second operational amplifier, VI- is a voltage signal produced by said second operational amplifier, V_X2 is a voltage signal applied to the first input terminal of said first operational amplifier, VI+ is the voltage signal Vout produced by said first operational amplifier, R₁ and R₂ are the resistance values of said first and second voltage divider resistors, respectively, R₃ and R₄ are the resistance values of said third and fourth voltage divider resistors, respectively, R_I is the resistance value of said input resistor, V_IN is an input voltage applied to the input resistor, R_F is the resistance value of said feedback resistor, V_OS1 is an offset voltage of said second operational amplifier, and AVDD is the voltage across the first and second voltage divider resistors.

5. An input signal amplifier for amplifying an input signal V_IN to provide an output signal VID, said input signal amplifier comprising:

a first operational amplifier configured to produce a first output voltage signal VI+;

a second operational amplifier configured to produce a second output voltage signal VI-;

said output signal VID comprising the difference between the absolute values of VI+ and VI- and being equal to;

##EQU8## first and second voltage divider resistors coupled in series, a first input terminal of said second operational amplifier coupled to a first node between said first and second voltage divider resistors;

third and fourth voltage divider resistors coupled in series, said third resistor being coupled to an output of said second operational amplifier, a first input terminal of said first operational amplifier coupled to a second node between said third and fourth voltage divider resistors;

a feedback resistor having a resistance R_F coupled between an output of said first operational amplifier and a second input terminal of said first operational amplifier;

an input resistor having a resistance R_I, said feedback resistor R_F being coupled in series with said input resistor having a resistance R_I ; and

a second input terminal of said first operational amplifier coupled to receive a voltage signal and, in response thereto, to generate said first output signal VI+.

6. The input signal amplifier recited in claim 5 including a feedback loop coupling an output of said second operational amplifier to a second terminal of said second operational amplifier.

7. The input signal amplifier recited in claim 6 wherein:

##EQU9## where V_X1 is a voltage signal applied to the first input terminal of said second operational amplifier, V_X2 is a voltage signal applied to the first input terminal of said first operational amplifier, R₁ and R₂ are resistance values of said first and second voltage divider resistors, respectively, R₃ and R₄ are resistance values of said third and fourth voltage divider resistors, respectively, V_OS1 is an offset voltage of said second operational amplifier, and AVDD is the voltage across the first and second voltage divider resistors.