Correction circuit for a digital quadrature-signal pair

• US 4,926,443 A
• Filed: 05/04/1989
• Issued: 05/15/1990
• Est. Priority Date: 05/27/1988
• Status: Expired due to Term

• Current Assignee: Deutsche ITT Industries GmbH
• Original Assignee: Deutsche ITT Industries GmbH
• Inventors: Reich, Werner
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Bocure, Tesfaldet
• Application Number:
  US07/347,379
• Time in Patent Office: 376 Days
• Field of Search: 375/60, 375/15, 375/39, 375/98, 375/102, 455/234, 455/304, 455/60, 329/320
• US Class Current: 375/349
• CPC Class Codes: H03D 1/2254 and a phase locked loop
• CPC Class Codes: H03D 2200/0047 Offset of DC voltage or frequency
• CPC Class Codes: H03D 3/006 by sampling the oscillations and further processing the samples, e.g. by computing techniques H03D3/007 takes precedence
• CPC Class Codes: H03D 3/008 Compensating DC offsets
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 25/062 Setting decision thresholds using feedforward techniques only
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal

Abstract

A correction circuit for a digital signal pair having an in-phase signal and a quadrature signal includes a value determining stage and an error-detecting stage. The value-determining stage determines a maximum value and a minimum value for the in-phase signal, a maximum value and a minimum value for the quadrature signal, and two held values for the quadrature signal that correspond to the maximum and minimum values of the in-phase signal. These signals are used in the error-detecting stage to derive an in-phase offset error signal, a quadrature offset error signal, a phase-error signal, and an amplitude-error signal from which an in-phase-offset-correcting signal, a quadrature-offset-correcting signal, a quadrature phase-correcting signal, and quadrature amplitude-correcting signal are formed by associated controllers.

Claims

1. A correction circuit for a digital signal pair having an uncorrecting in-phase signal and an uncorrecting quadrature signal, comprising:

an offset-correcting stage that receives said uncorrected in-phase signal and said uncorrected quadrature signal and that generates an offset-corrected in-phase signal and an offset-corrected quadrature signal, said offset-correcting stage further receiving an in-phase-offset-correcting signal and a quadrature-offset-correcting signal;

a phase-correcting stage that receives said offset-corrected in-phase signal and said offset-corrected quadrature signal and that generates an phase-corrected quadrature signal, said phase-correcting stage further receiving a phase-correcting signal;

an amplitude-correcting stage that receives said phase-corrected quadrature signal and that generates an amplitude-corrected quadrature signal, said amplitude-correcting stage further receiving an amplitude-correcting signal;

a value-determining stage comprising;

a first minimum detector that receives said offset-corrected in-phase signal and that generates an in-phase minimum value;

a first maximum detector that receives said offset-corrected in-phase signal and generates an in-phase maximum value;

a second minimum detector that receives said amplitude-corrected quadrature signal and generates a quadrature minimum value;

a second maximum detector that receives said amplitude-corrected quadrature signal and that generates a quadrature maximum value;

a first hold circuit that receives said amplitude-corrected quadrature signal, said first hold circuit responsive to said first minimum detector to store a first held quadrature value on the occurrence of said in-phase minimum value;

a second hold circuit that receives said amplitude-corrected quadrature signal, said second hold circuit responsive to said first maximum detector to store a second held quadrature value on the occurrence of said in-phase maximum value;

an error-detecting stage comprising;

a first adder that receives said in-phase maximum value from said first maximum detector and said in-phase minimum value from said first minimum detector, said first adder generating an in-phase offset error signal;

a second adder that receives said quadrature maximum value from said second maximum detector and said quadrature minimum value from said second minimum detector, said second adder generating a quadrature offset error signal;

a first subtracter having a minuend input that receives said second held quadrature value and having a subtrahend input that receives said first held quadrature value, said first subtracter generating a phase-error signal;

a second subtracter having a minuend input that receives said in-phase maximum value from said first maximum detector and having a subtrahend input that receives said in-phase minimum value from said first minimum detector, said second subtracter generating an in-phase amplitude value;

a third subtracter having a minuend input that receives said quadrature maximum value from said second maximum detector and having a subtrahend input that receives said quadrature minimum value from said second minimum detector, said third subtracter generating a quadrature amplitude value; and

a fourth substrater used as an amplitude comparator, said fourth subtracter having a minuend input that receives said quadrature amplitude value from said third subtracter and having a subtrahend input that receives said in-phase amplitude value from said second subtracter, said fourth subtracter generating an amplitude error signal; and

a first controller that receives said in-phase offset signal from said first adder and that generates said in-phase offset-correcting signal received by said offset-correcting stage;

a second controller that receives said quadrature offset error signal from said second adder and that generates said quadrature offset-correcting signal received by said offset-correcting stage;

a third controller that receives said phase-error signal generated by said first subtracter and that generates said phase-correcting signal received by said phase-correcting stage; and

a fourth controller that receives said amplitude-error signal generated by said fourth subtracter and that generates said amplitude-correcting signal received by said amplitude-correcting stage.

2. A correction circuit as defined in claim 1, wherein:

said first minimum detector comprises a third maximum detector, a first inverter and a second inverter, said third maximum detector having a signal input that receives said offset-corrected in-phase signal via said first inverter, said third maximum detector providing said in-phase minimum value as an output via said second inverter; and

said second minimum detector comprises a fourth maximum detector, a third inverter and a fourth inverter, said fourth maximum detector having a signal input that receives said amplitude-corrected quadrature signal via said second inverter, said fourth maximum detector providing said quadrature minimum value as an output via said fourth inverter.

3. A correction circuit as defined in claim 1, wherein at least one of said first and second maximum detectors comprises:

a memory for storing a maximum value, said memory being resettable to an initial value via a first reset signal;

a tracking stage comprising;

a fifth subtracter having a subtrahend input which receives said maximum value stored by said memory and having a minuend input that receives an input signal corresponding to the signal whose maximum value is being detected, said fifth subtracter providing an output signal having a sign bit that changes when said input signal increases to a value greater than said stored maximum value;

a sixth subtracter having a subtrahend input which receives said maximum value stored by said memory and having a minuend input that receives a preset value;

a first constant multiplier that receives the output of said fifth subtracter and multiplies said output by a first constant value;

a second constant multiplier that receives the output of said sixth subtracter and multiplies said output by a second constant value; and

a first electronic switch having first and second inputs and an output, said first input connected to the output of said second constant multiplier and said second input connected to the output of said first constant multiplier, said first electronic switch having a first position in which said first input of said first electronic switch is connected to said output of said first electronic switch and having a second position in which said second input of said first electronic switch is connected to said output of said first electronic switch, said first electronic switch responsive to the output signal of said fifth subtracter to assume said first position when the output signal of said fifth subtracter is less than zero and to assume said second position when the output signal of said fifth subtracter is greater than or equal to zero, said sign bit of the output signal of said fifth subtracter being said detector signal.

4. A correction circuit as defined in claim 3, wherein said memory for storing a maximum value comprises a first accumulator, said first accumulator comprising:

a first delay element having an input and an output, and having a reset input that receives a first reset signal, said first delay element being initialized to an initial value when said first reset signal is active, said output of said first delay element providing said maximum value; and

a third adder having first and second inputs and an output, said first input being connected to the output of said first electronic switch, and said second input being connected to the output of the first delay element, said output of said output of said third adder being connected to said input of said delay element.

5. A correction circuit as defined in claim 1, wherein said offset-correcting stage comprises:

a first offset-correcting stage adder having a first input that receives said uncorrected in-phase signal and having a second input that receives said in-phase-offset-correcting signal, said first offset-correcting stage adder having an output that provides said offset-corrected in-phase signal; and

a second offset-correcting stage adder having a first input that receives said uncorrected quadrature signal and having a second input that receives said quadrature-offset-correcting signal, said second offset-correcting stage adder having an output that provides said offset-corrected quadrature signal.

6. A correction circuit as defined in claim 1, wherein said phase-correcting stage comprises:

a phase-correcting stage multiplier having a first input that receives said offset-corrected in-phase signal, having a second input that receives said offset-corrected quadrature signal, and having an output that generates an output signal;

a phase-correcting stage adder having a first input that receives said offset-corrected quadrature signal, having a second input that receives said output signal from said phase-correcting stage multiplier and having an output that generates said phase-corrected quadrature signal.

7. A correction circuit as defined in claim 1, wherein said amplitude-correcting stage comprises:

an amplitude-correcting stage multiplier having a first input that receives said phase-corrected quadrature signal from said phase-correcting stage, having a second input that receives said amplitude-correcting signal from said fourth controller and having an output that generates an output signal; and

a fourth adder having a first input that receives said phase-corrected quadrature signal, having a second input that receives said output signal from said amplitude-correcting stage multiplier and having an output that generates said amplitude-corrected quadrature signal.

8. A correction circuit as defined in claim 1, wherein at least one of said first, second, third and fourth controllers comprises:

a control facility having a first input that receives a respective error signal, a second input that receives a blocking signal, a third input that receives an address word, a fourth input that receives a range-limit word, a fifth input that receives a respective correcting signal from the output of said controller, and an output; and

a second accumulator having a data input connected to said output of said control facility and having a reset input by which said accumulator can be initialized to a predetermined value in response to a second reset signal, said second accumulator storing a value that represents said respective correcting signal, said second accumulator having an output that provides said value as said respective correcting signal output from said respective controller.

9. A correction circuit as defined in claim 8, wherein said control facility comprises:

an increment memory having a plurality of data values stored therein, said increment memory addressable by said address word and providing one of said data values as an increment memory output value;

a first correction circuit inverter having an input that receives said increment memory output value and having an output that provides an inverted increment memory output value;

a second electronic switch having a first input and a second input, said first input connected to receive said increment memory output value from said increment memory, said second input connected to receive said inverted increment memory output value from said increment memory data inverter, said second electronic switch selecting one of said first and second inputs in response to the sign of said error signal;

a second correction circuit inverter having an input that receives said range-limit and having an output that provides an inverted range-limit word;

a first comparator having a subtrahend input that receives said range-limit word directly from said fourth input, having a minuend input that receives said respective correcting signal from said second accumulator, and having an output that provides an output signal; and

a second comparator having a minuend input that receives said inverted range-limit word from said second correction circuit inverter, having a subtrahend input that receives said output signal from said second accumulator, and having an output that provides an output signal;

a first AND-gate having a first input that receives said error signal, having a second input that receives said output from said first comparator, and having an output that provides an output signal;

a second AND-gate having an inverting first input that receives said error signal, having a second input that receives said output from said second comparator, and having an output that provides an output signal;

an OR-gate having a first input that receives said blocking signal, having a second input that receives said output signal from said first AND-gate, having a third input that receives said output signal from said second AND-gate, and having an output that generates an output signal; and

a third electronic switch having a first input that receives a data value of 0, having a second input that receives said output signal from said second accumulator, and having an output that is connected to the data input of said second accumulator, said third electronic switch further having a control input that receives said output signal from said OR-gate, said output signal from said OR-gate controlling the selection of said first input or second input by said third electronic switch.

10. A correction circuit as defined in claim 1, further including a low-IF conversion circuit that provides said digital signal pair from an input signal having a carrier frequency, said low-IF conversion circuit comprising:

a first RF mixer that provides said uncorrected in-phase signal;

a second RF mixer that provides said uncorrected quadrature signal; and

a local oscillator that generates a 0°

signal that drives said first RF mixer and a 90°

signal that drives said second RF mixer, said 0°

signal and said 90°

signal generated by said local oscillator having a frequency that lies in the useful band of the RF signal and is separated from the actual carrier frequency by a predetermined distance.