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Correction of I/Q channel errors without calibration

Imported: 23 Feb '17 | Published: 22 Oct '02

Armin W. Doerry, Bertice L. Tise

USPTO - Utility Patents

Abstract

A method of providing a balanced demodular output for a signal such as a Doppler radar having an analog pulsed input; includes adding a variable phase shift as a function of time to the input signal, applying the phase shifted input signal to a demodulator; and generating a baseband signal from the input signal. The baseband signal is low-pass filtered and converted to a digital output signal. By removing the variable phase shift from the digital output signal, a complex data output is formed that is representative of the output of a balanced demodulator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form part of the specification, illustrate an embodiment of the present invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 shows a prior art circuit for video-frequency offset phase-history collection.

FIGS. 2A-2C show a signal at various locations on the circuit of FIG.

1.

FIG. 3 shows a doppler offset phase-history collection circuit.

FIGS. 4A-4C show phase-history plots for the circuit of FIG.

3.

FIG. 5 shows a phase modulated I/Q demodulator of the invention.

Claims

1. A method of providing a balanced demodular output comprising:

2. The method of claim 1 wherein the analog pulsed input has a pulse repetition rate f

p.

3. The method of claim 2 wherein the variable phase shift changes only over a range of discrete values.

4. The method of claim 3 wherein the variable phase shift changes with each pulse.

5. The method of claim 4 wherein the variable phase shifts by 90° with each change.

6. The method of claim 3 wherein removing the variable phase shift comprises mixing the digital output signal with a digital local oscillator signal having a variable phase that is complementary to the variable phase shift on the input signal.

7. The method of claim 6 wherein the variable phase shifts by 90° with each change and the digital local oscillator signal shifts by −j with each change.

8. The method of claim 2 wherein the demodulator has a single channel and a single analog-digital converter for converting the baseband signal to the digital output signal.

9. The method of claim 2 wherein the demodulator has parallel I and Q channels, each channel having an analog-digital converter having a digital output, these digital outputs being combined to form the digital output signal.

10. The method of claim 9 wherein f

p≧2B

Doppler, where B

Doppler is the Doppler bandwidth of the signal.

11. The method of claim 10 further comprising band pass filtering the digital output.