US 8,446,143 B2 · Self-calibration circuit with gyrated output impedance

Abstract

Various embodiments of a self-calibration circuit may solve the problem that arises in high performance oscilloscopes and in particular, RF oscilloscopes, of internally providing a precision calibration signal without degrading the bandwidth, flatness of the frequency response, and input return loss of the oscilloscope. The self-calibration circuit may be configured to implement an impedance transformation technique where active and passive circuit elements with carefully chosen values are configured in an impedance converter. During self-calibration, switching elements comprised in the self-calibration circuit may be toggled to create a servo loop comprising an amplifier within the circuit, with an attenuator and resistive component acting as feedback elements. The circuit may hence become an impedance gyrator and behave as a precision source with an impedance matching the input impedance of the load circuit.

Claims20

Dependent claims

A circuit comprising:

an attenuator having a first terminal and a second terminal, and configured to couple to a load via a third terminal;
an amplifier having a first input configured to receive a calibration signal, and further having a second input and an output;
a switching circuit for switching between normal operating mode and calibrating operating mode, configured to switchably couple the first terminal of the attenuator to the second input of the amplifier and the second terminal of the attenuator to the output of the amplifier to form a servo loop comprising the amplifier with the attenuator as a feedback element, wherein the servo loop operates as a precision signal source having an output impedance that matches an impedance of the load, to deliver the calibration signal to the load.

A self-calibration system comprising:

means for providing a calibration signal to a first input of an amplifier;
means for coupling an attenuator to a load;
and
means for switching between normal operating mode and calibrating operating mode, comprising:
means for connecting a feedback path between an output of the amplifier and a second input of the amplifier, and including the attenuator in the feedback path to deliver the calibration signal to the load when switching from normal operating mode to calibrating operating mode;
and
means for developing, between the first input of the amplifier and the load, a total impedance that matches an impedance of the load when switching from normal operating mode to calibrating operating mode.

4 more elements

A system comprising:

an attenuator having a first terminal configured to receive a user input signal, and a second terminal configured to couple to a load;
an amplifier having a first input configured to receive a calibration signal;
a first switching element configured with two selectable switching configurations, wherein the first switching configuration couples the first terminal of the attenuator to a second input of the amplifier, and the second switching configuration couples the first terminal of the attenuator to an output of the amplifier;
a second switching element configured with two selectable switching configurations, wherein the first switching configuration couples a third terminal of the attenuator to the output of the amplifier, and the second switching configuration couples the third terminal of the attenuator to reference ground;
wherein a combination of the first switching configuration for the first switching element and the first switching configuration for the second switching element establishes a servo loop comprising the amplifier with the attenuator as a feedback element, wherein the servo loop operates as a precision signal source having an output impedance that matches an impedance of the load, to deliver the calibration signal to the load.

2 more elements

Dependencies are inferred from the claim text.

Self-calibration circuit with gyrated output impedance

Life of this patent

Self-calibration circuit with gyrated output impedance

Life of this patent

Abstract

Claims20