US 5,554,943 AGranted

Analog to digital converter having a magnitude amplifier with an improved differential input amplifier

AssigneeAnalog Devices, Inc.

InventorCarl W. Moreland

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Abstract

An improved magnitude amplifier (magamp) is provided for a serial-type A/D converter. The magamp includes an improved differential input amplifier circuit to which offset circuitry is connected. These elements may be implemented in a single integrated circuit chip or as separate discrete circuits in hardware. The differential input amplifier circuit includes two pairs of differential input transistors, a comparator, and current switching control transistors. The comparator provides outputs that drive the current switching control transistors. The current switching control transistors are connected below the input transistors and not above the input transistors to reduce the parasitic capacitive loading at the outputs of the differential input amplifier circuit and increase the speed of the magamp. The offset circuitry provides the appropriate signals for aligning the output signals for output to the next stage magamp.

Claims20

Dependent claims

A magnitude amplifier (magamp), comprising:

a differential input circuit for receiving and amplifying a differential analog input, with the differential input circuit having a receiving circuit having a first branch and a second branch;
a current switching control circuit connected to the first and second branches of the differential input circuit on a first side of the receiving circuit, with the current switching control circuit having a first portion connected to the first and second branches of the differential input circuit and a second portion connected to the first and second branches of the differential input circuit, the current switching control circuit for controlling folding of the differential analog input at a predetermined relationship between the signals of the differential analog input;
a comparator for receiving the differential analog input and generating a first and second output, with a first output controlling first sections of the first and second portions of the current switching control circuit, and the second output controlling second sections of the first and second portions of the current switching control circuit;
first output means that connects to the first branch on a second side of the receiving circuit, the first output means for providing as an output from the first branch a first output signal generated at least in part under control of the current switching control circuit;
and
second output means that connects to the second branch on the second side of the receiving circuit, the second output means for providing as an output from the second branch a second output signal generated at least in part under control of the current switching control circuit.

3 more elements

An analog to digital converter comprising:

a plurality of cascaded amplifiers, each including:
a receiving circuit for receiving and amplifying a differential analog input,
a comparator for receiving the differential analog input, for comparing input signals, and for generating first and second control signals based on the comparison,
a current switching control circuit connected to the receiving circuit on a first side, the current switching control circuit for controlling folding of the differential analog input in response to the first and second control signals, and
an output circuit, connected to the second side of the receiving circuit, for providing a first output signal and a second output signal, the first and second output signals generated at least in part under control of the current switching control circuit,
wherein the amplifiers are cascaded such that the first and second output signals from one amplifier are provided as the differential analog input to a next amplifier;
and
a gray-to-binary converter coupled to the plurality of cascaded amplifiers for receiving as inputs the first and second control signals from each of the amplifiers, and for providing a parallel digital output.

5 more elements

Dependencies are inferred from the claim text.