Back to results
US 4,910,800 AGranted
Dual branch receiver with wobbled oscillator for distortion reduction
AssigneeU.S. Philips Corporation
InventorKah-Seng Chung
Life of this patent
Estimating the term…
Abstract
A dual branch receiver in which the frequency of the first local oscillator (32) is offset by a few hundred hertz from the input carrier in order to provide separate wanted and image components. Gain and phase control are provided to compensate for differences between the two branches (12, 14), the image signal being used to provide the required error signals. However in the event of the modulation frequency being equal to the offset frequency, the image signals cannot be distinguished from the wanted signals thus inhibiting gain and phase control. This drawback is overcome in the receiver in accordance with the present invention by wobbling the frequency provided by the first local oscillator (28). The wobbling frequency is preferably sub-audible so as not to be discernable to the ear.
Claims18
A dual branch receiver for an incoming signal having a carrier frequency, comprising:
- a signal input terminal coupled to first and second branches, the first branch including first and third mixers, the second branch including second and fourth mixers, said incoming signal being coupled to said first and second mixers, and said third and fourth mixers having outputs,
- a first local oscillator for producing a first local oscillator signal which is supplied to the first and second mixers for frequency down converting said incoming signal, the first local oscillator frequency being offset from said carrier frequency by a given offset frequency,
- a first 90.degree. phase shifter for providing a quadrature phase relationship between one of the signals applied to the first mixer and the corresponding signal applied to the second mixer, whereby output signals from the first and second mixers are quadrature related signals, said quadrature related signals being coupled respectively to the third and fourth mixers,
- a second local oscillator for producing a second local oscillator signal which is applied in quadrature to the third and fourth mixers for frequency up converting said quadrature related signals,
- a summing circuit and a differencing circuit each having inputs coupled to said outputs of the third and fourth mixers, and
- a control signal arrangement receiving signals from at least one of said summing and differencing circuits for generating respective control signals for correcting undesired differences in signal processing in said first and second branches,
- characterized in that said receiver further comprises means for frequency modulating the first local oscillator signal with a wobbling frequency less than said given offset frequency, whereby distortion in output signals from said summing circuit and said differencing circuit is minimized when said incoming signal includes modulation components having frequencies related to said given offset frequency.
4 more elements
A dual branch receiver for an incoming signal having a carrier frequency, comprising:
- a signal input terminal coupled to first and second branches, the first branch including first and third mixers, the second branch including second and fourth mixers, said incoming signal being coupled to said first and second mixers, and said third and fourth mixers having outputs,
- a first local oscillator for producing a first local oscillator signal which is supplied to the first and second mixers for frequency down converting said incoming signal, the first local oscillator frequency being offset from said carrier frequency by a given offset frequency,
- a first 90.degree. phase shifter for providing a quadrature phase relationship between one of the signals applied to the first mixer and the corresponding signal applied to the second mixer, whereby output signals from the first and second mixers are quadrature related signals, said quadrature related signals being couupled respectively to the third and fourth mixers,
- a second local oscillator for producing a second local oscillator signal which is applied in quadrature to the third and fourth mixers for frequency up converting said quadrature related signals,
- a summing circuit and a differencing circuit each having inputs coupled to said outputs of the third and fourth mixers, and
- a control signal arrangement receiving signals from at least one of said summing and differencing circuits for generating respective control signals for correcting undesired amplitude and phase differences in signal processing in said first and second branches, said arrangement including means for detecting an unwanted image signal component separated from the second local oscillator signal frequency by a value equal to the offset frequency,
- characterized in that said receiver further comprises means for frequency modulating the first local oscillator signal with a wobbling frequency less than said given offset frequency, said means for detecting thereby detecting said unwanted image signal component in the presence of frequency modulation of said incoming signal at a modulation frequency equal to said given offset frequency, whereby distortion in output signals from said summing circuit and said differencing circuit is minimized when said incoming signal is frequency modulated at a modulation frequency equal to said given offset frequency.
4 more elements
Dependencies are inferred from the claim text.