# US 2014/0192844 A1 · Fully integrated dc offset compensation servo feedback loop

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- Number: US 2014/0192844 A1
- Document ID: US20140192844A1
- Status: Published application
- Kind: A1
- Application number: 13/737,915
- Filed: 2013-01-09
- Published: 2014-07-10
- Earliest claimed: 2013-01-09
- Assignees: King Abdulaziz City for Science and Technology; King Fahd University of Petroleum and Minerals
- Applicants: King Fahd University of Petroleum and Minerals; King Abdulaziz City for Science and Technology
- Inventors: HUSSAIN ALZAHER
- Web page: https://patentgrep.com/patent/US20140192844A1

## CPC

- H04L 25/063: {Setting decision thresholds using feedback techniques only}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

The fully integrated DC offset compensation servo feedback loop is an integrator that measures the output signal DC component, and then feeds back and subtracts the measured DC component from the input signal. A larger integrator time constant lowers the high pass corner frequency, which must be very small in order to minimize the loss of the low frequency component of the desired signals. The large time constant is achieved on an integrated circuit by the use of a class-AB fully differential opamp in conjunction with an R-2R ladder as a circuit element to accomplish an integrated large time constant integrator. The R-2R ladder is configured as a digitally programmable resistor.

## Claims

### Claim 1

A fully integrated DC offset compensation servo feedback loop, comprising:
a differential dual op amp integrated circuit having a negative input terminal, a positive input terminal, a positive output terminal, and a negative output terminal;
first and second RC circuits configuring the integrated circuit as a differential integrator, the first RC circuit having a first digitally programmable R-2-R ladder forming the resistive component of the RC circuit, the negative input terminal being connected between the resistive and capacitive components of the first RC circuit, and the second RC circuit having a second digitally programmable R-2-R ladder forming the resistive component of the RC circuit, the positive input terminal being connected between the resistive and capacitive components of the second RC circuit;
wherein the servo feedback loop is adapted for connection to a high-gain, low pass network in summation circuitry that sums with signals having a DC offset component input, the positive output terminal and the negative output terminal of the op amp integrated circuit being adapted for connection at first and second inputs, respectively, of the high-gain, low pass network, first and second outputs of the high gain low pass network being adapted for connection as differential inputs to the op amp integrated circuit through the first and second R-2-R ladders, respectively, the servo feedback loop being configured for substantially attenuating the DC offset component from the signals summed in the high-gain, low pass network.

### Claim 2 (depends on 1)

The fully integrated DC offset compensation servo feedback loop according to claim 1, further comprising means for programmably switching individual branches of said first and second R-2-R ladders to ground, thereby individually adjusting total resistance of said first R-2-R ladder and total resistance of said second R-2-R ladder.

### Claim 3 (depends on 1)

The fully integrated DC offset compensation servo feedback loop according to claim 1, wherein said differential dual op amp integrated circuit comprises a class-AB fully differential operational amplifier circuit.

### Claim 4

A transceiver with servo feedback loops for compensating for DC offset in transmitted and received signals, comprising:
a direct conversion frequency-shift-keyed (FSK) transceiver, the transceiver having a front end modulating and demodulating signals when transmitting and receiving signals, the front end having a filter for transmitted signals and a filter for received signals, the front end mixing an unwanted DC offset component onto the transmitted and received signals; and
a first servo feedback loop connected across the filter for transmitted signals and a second servo feedback loop connected across the filter for received signals, each of the servo feedback loops having a differential dual operational amplifier integrated circuit configured as a differential integrator, each of the operational amplifiers in the integrated circuit having an RC circuit connected thereto, each of the RC circuits having a digitally programmable R-2-R ladder forming the resistive component of the RC circuit; and
wherein the differential integrator measures the unwanted DC offset and the R-2-R ladders are programmable to compensate for the unwanted DC offset.