Low noise, bandwidth compensated transimpedance amplifier

What is claimed is:

1. A low noise preamplifier circuit comprising:

a differential amplifier having a complimentary input and a complimentary output;

a first resistor and a second resistor, said first resistor and second resistor being coupled across said differential amplifier from input to output, providing negative feedback, said first resistor and second resistor having a substantially equal resistance value; and

a first capacitor and a second capacitor, said first capacitor and said second capacitor being coupled across said differential amplifier from input to output providing positive feedback, said first capacitor and said second capacitor having a substantially equal capacitance value, said capacitance value being selected to provide bandwidth compensation for an input capacitance applied to said complimentary input, wherein said resistance value is related to said capacitance value by the equation, CP≅2Ci/A-1/(2πB⋅Rf), where Cp is said capacitance value, Ci is the value of the input capacitance, A is a gain of said differential amplifier circuit, B is a selected operating bandwidth and Rf is said resistance value.

2. A low noise preamplifier circuit compensated for an applied input capacitance, the preamplifier comprising:

an amplifier circuit;

a first resistor and a second resistor for providing negative, resistive feedback across said amplifier circuit, said first resistor and second resistor having a substantially equal resistance value; and

a first capacitor and a second capacitor for providing positive, capacitive feedback across said amplifier circuit, said first capacitor and said second capacitor having a substantially equal capacitance value, wherein said resistance value is related to said capacitance value, said relationship being substantially defined by the equation CP≅2Ci/A-1/(2πB⋅Rf), where Cp is said capacitance value, Ci is the value of the input capacitance, A is a gain of said differential amplifier circuit, B is a selected operating bandwidth and RF is said resistance value.


3. A low noise, bandwidth compensated optical front end circuit comprising:

a differential amplifier circuit, said differential amplifier circuit having a first input terminal, a second input terminal, a first output terminal and a second output terminal;

a photodetector having an associated capacitance value, said optical detector being operatively coupled to said first input terminal and said second input terminal of said differential amplifier circuit;

a first resistor, said first resistor connected between said first input terminal and said first output terminal;

a second resistor, said second resistor connected between said second input terminal and said second output terminal;

a first capacitor, said first capacitor being connected between said first output terminal and said second output terminal; and

a second capacitor, said second capacitor being connected between said second input terminal and said first output terminal, said first capacitor and said second capacitor having a substantially equal capacitance value, said value selected to compensate the effect of the capacitance value associated with said photodetector, wherein the value of said first resistor and said second resistor is related to the value of said first capacitor and said second capacitor, said relationship being substantially defined by the equation CP≅2Ci/A-1(2πB⋅Rf), where Cp is the value of said first and second capacitor, Ci is the value of the capacitance of said photodetector, A is a gain of said differential amplifier circuit, B is a selected operating bandwidth and Rf is the value of said first and second resistors.

4. A method of compensating an amplifier circuit in the presence of an applied input capacitance comprising the steps:

determining a gain of the amplifier, a transimpedance resistance value in feedback with the amplifier and a value of the input capacitance;

selecting a desired operating bandwidth of the amplifier; and

calculating a value of at least one compensation capacitor applied in a positive feed back arrangement across the amplifier by applying a formula, CP≅2Ci/A-1(2πB⋅Rf), where Cp is the value of said compensation capacitor, Ci is the value of the input capacitance, A is a gain of the amplifier circuit, B is the selected bandwidth and Rf is the value of the transimpedance resistance.

Nombre: Carlos L. Briceño R
Materia: CRF
Fuente: http://www.patentstorm.us/patents/5982232/description.html