Direct conversion receiver per-selection

Details Direct conversion receiver per-selection Direct conversion receiver per-selection

1998-12-02

2001-03-27

Eisenzopf, Reinhard (Department: 2682)

Telecommunications

Receiver or analog modulated signal frequency converter

Frequency modifying or conversion

C455S307000, C455S339000

Reexamination Certificate

active

06208850

ABSTRACT:

This invention relates to direct conversion receivers and in particular it relates to an arrangement for control of a pre-selection bandpass filter.
FM receivers constructed to convert incoming radio frequency (RF) modulation directly to the baseband are well known and the prior art is described e.g. in U.S. Pat. No. 4,653,117.
In direct conversion receivers, the frequency of a local oscillator in the receiver is made equal to the incoming RF carrier frequency such that the modulation of the incoming signal is converted directly to baseband.
A pre-selection filter as referred to herein is a band pass filter operating at the RF frequency and preceding the first down conversion stage of the receiver channel. The purpose of the pre-selection filter is to remove large unwanted signals.
The filter normally used would be a ceramic or surface acoustic wave type set to operate at fixed frequency and having a bandwidth to cover the working band of interest e.g. 25 MHz for GSM. Within the working band of interest there is a number of channels, the bandwidths of these channels being much less than the working band e.g. 200 KHz channel bandwidth for GSM.
The extent of the bandwidth of the pre-selection filter has an effect such that the selectivity of this filter largely determines the performance of the receiver. A minimum bandwidth for the pre-selection filter, consistent with adequate reception of the wanted signal would enhance receiver performance considerably.
It is an object of the invention to provide a simple tunable band pass filter capable of implementation as an integral part of an ASIC receiver.
A pre-selector filter of narrow bandwidth (e.g. 1 MHz for the GSM example given above), with the ability to track the single channel of interest at any one time would therefore greatly improve receiver performance.
According to the invention there is provided A tunable pre-selector filter for a direct conversion receiver comprising a voltage controlled band pass filter, receiving an RF input and feeding the filtered RF from the voltage controlled band pass filter as an input to a mixer for mixing with an output of a local oscillator, the output of the local oscillator being fed also to a phase detector for comparison with a local oscillator output obtained as leakage from the mixer having passed through the voltage controlled band pass filter and an output from the phase detector applied through a loop filter as a control voltage to the voltage controlled band pass filter.


REFERENCES:
patent: 4965853 (1990-10-01), Barnard
patent: 5781851 (1998-07-01), Saito
patent: 5943370 (1999-08-01), Smith
patent: 991505 (1965-05-01), None
patent: 2 040 615 (1980-08-01), None
patent: 2 101 822 (1983-01-01), None

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