US 4,953,182 A · Gain and phase correction in a dual branch receiver

Abstract

A dual branch receiver consists of first and second branches (12, 14) respectively comprising first and third mixers (16, 20) and second and fourth mixers (17, 21). An input terminal (10) for a signal having a carrier frequency (.omega..sub.c) is connected to the first and second paths. A first local oscillator frequency (.omega..sub.o) is supplied in quadrature to the first and second mixers (16, 17), where .omega..sub.c -.omega..sub.o =.DELTA..omega. and .DELTA..omega. is of the order of 2.pi..times.100 radians/sec. A second local oscillator (30) frequency is supplied in quadrature to the third and fourth mixers (20, 21). An output signal is derived by connecting a sum circuit (22) and a difference circuit (24) to the first and second branches. The outputs of the sum and difference circuits (22, 24) are also used to provide gain and phase correction signals. It has been found that if the correction signals are based on signals centered on 2.DELTA..omega. then they are substantially free of ripple. The gain correction is derived by mixing the 2.DELTA..omega. signals derived by multiplying difference by difference (or sum by sum) with the 2.DELTA..omega. signals derived by multiplying sum by difference and low pass filtering. The phase correction is derived by mixing a 90.degree. phase shifted difference signal with the sum signal (or vice versa) and deriving the 2.DELTA..omega. signals which are mixed with 2.DELTA..omega. signals derived by multiplying the difference by difference (or sum by sum) and low pass filtering.

Claims20

Dependent claims

A dual branch receiver comprising:

a signal input terminal for an input signal having a carrier frequency (.omega..sub.c),
a first branch including first and third mixers,
a second branch including second and fourth mixers,
two arithmetic combiners for combining signals from said branches to provide respective first and second combiner outputs, the first and second mixers each having a signal input coupled through a respective input signal path to the signal input,
a first local oscillator for producing a local oscillator signal (.omega..sub.o) couples through respective oscillator signal paths to the first and second mixers,
a first 90.degree. phase shifter provided in one of the signal paths to the second mixer, the third and fourth mixers being coupled to the first and second mixers, respectively, for receiving a down converted signal therefrom,
a second local oscillator coupled to the third mixer and coupled through a quadrature phase shifter to the fourth mixer, one of said arithmetic combiners being a summing means for obtaining the sum of the signals at the outputs of the third and fourth mixers, the other of said arithmetic combiners being a differencing means for obtaining the difference between the signals at the outputs of the third and fourth mixers, and
means for correcting gain and phase errors in said branches, said correcting means being coupled to the summing and differencing means for transforming the outputs thereof to produce signals having terms centered on 2.DELTA..omega., where .DELTA..omega. equals (.omega..sub.o -.omega..sub.c).

5 more elements

Dependencies are inferred from the claim text.

Gain and phase correction in a dual branch receiver

Life of this patent

Gain and phase correction in a dual branch receiver

Life of this patent

Abstract

Claims20