US 6,144,244 A · Logarithmic amplifier with self-compensating gain for frequency range extension

Abstract

A progressive-compression logarithmic amplifier, amplifier stage, and method for increasing the bandwidth of a differential-input progressive-compression logarithmic amplifier are disclosed. The amplifier stage provides positive gain increases for decreases in the impedance of the load driven by the stage. When multiple amplifier stages of this type are cascaded, the gain increase in each stage compensates for high-frequency roll-off due to the input capacitance of the following stage. The compensating is activated by the roll-off effect itself, making the device self-compensating. This is preferably accomplished by providing a drive current sensing path that makes each node of the stage's differential output respond in opposition to the drive current drawn at the stage's other differential output--that is, an increase in drive current at one output node drops the voltage at the other output node.

Claims21

Dependent claims

An amplifier stage comprising:

a differential input gain section for generating a differential output signal, responsive to an input signal, at a pair of differential output nodes;
a first output buffer coupled to the input gain section at one of the output nodes;
and
a second output buffer coupled to the input gain section at the other of the output nodes;
wherein the first and second buffers are configured to automatically adjust the stage gain to compensate for changes in the output load impedance presented to the stage.

2 more elements

A method for increasing the bandwidth of a differential-input progressive-compression logarithmic amplifier, comprising the steps of:

amplifying, through a differential-pair amplifier having two load paths, a differential voltage input at a first stage of the logarithmic amplifier, thereby producing an amplified differential voltage output at a pair of differential-pair output nodes, one node in each load path;
buffering the amplified differential voltage output through a pair of output buffers, one inserted between one of the differential-pair output nodes and one of the stage differential voltage outputs, and the other inserted between the other of the differential-pair output nodes and the other of the stage differential voltage outputs, thereby supplying drive current to the differential voltage inputs of a second stage of the logarithmic amplifier through the pair of output buffers of the first stage;
sensing the drive current required at each differential voltage input of the second stage;
and
responding to an increase in drive current required at one differential voltage input of the second stage by changing the voltage at the other differential voltage input of the second stage.

2 more elements

Dependencies are inferred from the claim text.

Logarithmic amplifier with self-compensating gain for frequency range extension

Life of this patent

Logarithmic amplifier with self-compensating gain for frequency range extension

Life of this patent

Abstract

Claims21