Radio receiver and method of operation

Details Radio receiver and method of operation Radio receiver and method of operation

1998-05-28

2001-11-13

Maung, Nay (Department: 2681)

Telecommunications

Receiver or analog modulated signal frequency converter

Local control of receiver operation

C455S226200, C455S240100, C455S067150, C375S345000

Reexamination Certificate

active

06317589

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a radio receiver, in particular but not exclusively, to a gain compensation loop for a quadrature receiver.
The current trend in receiver technology is to reduce weight, volume, power consumption and cost. This is particularly important for receivers in portable apparatus such as radio telephones. This has resulted in receiver architecture designs in which there are no or few discrete radio frequency (RF) and intermediate frequency (IF) filters in the receiver front end.
An example of a receiver architecture having few discrete RF and IF filters is a single conversion low-IF architecture for a quadrature receiver. Single conversion low-IF architectures typically produce an image signal which is very close to the wanted signal. Such image signals are termed “in-band” image signals, and may be filtered out using a single sideband filter. However, a portion of the image signal appears at the wanted signal frequency as cross-talk if there is an imbalance between the phase and/or gain of respective quadrature signals. It is desirable for such cross-talk to be reduced or rejected. Typically, a quadrature receiver front end can only achieve about 30dB of image-to-signal cross-talk rejection, which is often insufficient for many applications such as radio telephones.
A solution to the problem of cross-talk is to use a double-quadrature mixer architecture. However, such an architecture requires 90° phase shifts on both the local oscillator and RF ports coupled to four mixers. Providing at least one of the ports (e.g. the local oscillator) is phase and amplitude balanced, any imbalance at the other port (e.g. the RF port) results in a spurious product at a frequency given by the sum of the RF and local oscillator frequencies. This can be easily filtered out using an RF bandpass filter before the mixers.
A drawback of the above approach is that four mixers are required resulting in relatively high power consumption. Additionally, a relatively bulky RF 90° hybrid coupler is also required together with quadrature balance on the local oscillator port.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a gain compensation loop for a quadrature receiver adapted to generate first and second quadrature signals from a received signal, the gain compensation loop comprising : a signal strength comparator for receiving the first and second signals and adapted to output a third signal indicative of a difference in signal strength between the first and second signals; and gain adjusting means for adjusting the strength of the first signal in accordance with the third signal thereby bringing the first and second signals towards the same strength.
According to a second aspect of the invention there is provided a method for gain compensation in a quadrature receiver adapted to generate first and second quadrature signals from a received signal, the method comprising the steps of: comparing the signal strength of the first signal with the signal strength of the second signal; deriving a third signal indicative of a difference in strength between the first and second signals; and adjusting the strength of the first signal in accordance with the third signal.
Preferred embodiments in accordance with first and second aspects of the invention have the advantage that the strength of the first and second signals may be brought towards a balance by appropriate control of the gain adjusting means. Thereby image cross-talk may be reduced. This obviates the need for image rejection filters in the RF front end of the receiver which results in lower weight, volume, loss and cost for such receivers.
In a preferred embodiment the gain adjusting means is disposed in the radio frequency front end of a quadrature receiver which has the advantage that any image rejecting filters in the intermediate frequency region of the receiver are less likely to be overdriven by a strong image signal.
Preferably, the gain adjusting means comprises variable gain mixer, which is suitably one of the mixers in the quadrature receiver.
Optionally, the gain adjusting means is disposed after the radio frequency front end and is operable for signals at an intermediate frequency of a quadrature receiver. Such an intermediate frequency may be zero Hertz (0 Hz) for a gain compensation loop in a direct conversion receiver, for example.
Suitably, the gain adjusting means and/or gain comparator comprise an appropriately conditioned digital signal processor, which advantageously is environmentally independent and does not require external components. Alternatively, the gain adjusting means comprises an amplifier.
The gain compensation loop may comprise a loop filter having an input for receiving the third signal and an output for providing a control signal to the gain adjusting means, thereby providing for tracking a dynamic gain or signal strength imbalance between first and second signals.


REFERENCES:
patent: 4584710 (1986-04-01), Hansen
patent: 4856027 (1989-08-01), Nakamura et al.
patent: 4922549 (1990-05-01), Johnson et al.
patent: 4955078 (1990-09-01), Chung
patent: 5052050 (1991-09-01), Collier et al.
patent: 5481226 (1996-01-01), Parkes, Jr.
patent: 5604929 (1997-02-01), Loper et al.
patent: 5696819 (1997-12-01), Suizu et al.
patent: 5848104 (1998-12-01), Ishizu
patent: 5854973 (1998-12-01), Holtvoeth
patent: 5926749 (1999-07-01), Igarashi et al.
patent: 0305 603 A1 (1989-03-01), None
patent: 411017748A (1999-01-01), None
“Yu Hewhu Cordic-Base VLSI Architectures for Digital Signal Processing” IEEE Signal Processing Magazine, pp. 16 to 35, Jul. 1992.
United Kingdom Search Report.

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