Communication signal receiver and an operating method therefor

Details Communication signal receiver and an operating method therefor Communication signal receiver and an operating method therefor

1999-11-19

2003-08-19

Bost, Dwayne (Department: 2681)

Telecommunications

Receiver or analog modulated signal frequency converter

Noise or interference elimination

C455S226100, C455S226200, C455S229000, C455S421000, C375S319000

Reexamination Certificate

active

06608999

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a communication signal receiver with a plurality of components arranged along at least one signal path, where the components along the or each signal path comprise a filter for processing a received signal and averaging means for deriving a mean value of the signal. The invention also relates to a method of operating a communication signal receiver with a plurality of components arranged along at least one signal path, wherein a received signal is converted to a digital form and the signal is processed by at least one digital filter comprised in said plurality of components.
DESCRIPTION OF THE PRIOR ART
Communication signal receivers as set out above are used in e.g. wireless telecommunication devices, such as mobile telephones.
A generic communication signal receiver according to the prior art is shown in FIG.
4
. The receiver is a homodyne receiver comprising dual communication channels, which are commonly known as I and Q channels. The dual-channel homodyne receiver of
FIG. 4
is of a kind, which is frequently used in contemporary digital mobile telephones, such as GSM, DCS or PCS telephones.
The receiver comprises an antenna
400
for receiving an incoming electromagnetic communication signal, such as a TDMA signal (“Time Division Multiple Acces”) representing a stream of digital data symbols, which have been modulated onto two orthogonal carrier waves. The received signal is fed through a bandpass filter
402
, amplified in an amplifier
404
and then split into two identical signals in a splitter
406
. The first of these signals goes to a first signal path, where it is initially mixed in a mixer
420
a
with an intermediate frequency signal. The intermediate frequency signal is fed from a local oscillator
410
and passes unmodified through a phase shifter
408
. Similarly, the second signal goes to a second signal path, where it is mixed in a mixer
420
b
with the intermediate frequency signal from the local oscillator
410
, once the phase of the intermediate frequency signal has been shifted by 90° in the phase shifter
408
.
The output of the mixer
420
a
is filtered by a lowpass filter
422
a
and amplified in a second amplifier
424
a
. Subsequently, the signal is fed to an AD converter
426
a
for sampling the signal and converting it to a digital signal comprising aforesaid stream of data symbols. The digital signal is filtered in a digital lowpass filter
430
a
, and the digital data symbols contained in the signal are supplied, at a node
432
a
, to a digital memory
450
. An average calculator
439
a
determines the mean value (DC level) of the digital signal and supplies the mean value to a negative input of an adder
440
a
. At a positive input the adder receives the digital data symbols, that were previously tapped from the signal path at node
432
a
. Thus, the adder
440
a
will in effect subtract the signal mean value, as determined by the average calculator
439
a
, from the digital signal.
Consequently, the output of the adder
440
a
at the end of the first signal path will finally provide a first part of the stream of digital data symbols, that were contained in and carried by the analog signal initially received at the antenna
400
. Correspondingly, the second signal path, starting with a mixer
420
b
and ending with an adder
440
b
, will provide a second part of the stream of digital data. The stream of digital data symbols are subsequently used by other components in the mobile telephone for producing e.g. an audible output through a loudspeaker, such as speech from a party with which the user of the telephone is currently having a telephone conversation. Alternatively, the stream of digital data symbols may represent data messages sent between two computers during a data communication session.
PROBLEM
The use of digital filters
430
a-b
introduces a delay in the signal path, due to the inherent operational properties of digital filters, such as FIR (Finite Impulse Response) or IIR (Infinite Impulse Response) filters. Ideally, once the last wanted digital data symbol has been sampled, the components prior to the digital filters (such as the mixers
420
a-b
, the amplifiers
404
a-b
,
424
a-b
and the AD converters
426
a-b
) should be switched to a passive or idle mode, in order to preserve power and/or to enter a transmit mode as soon as possible.
However, switching off the receiver circuits immediately after the last wanted data symbol has been sampled causes transient noise from the digital filter, due to the rapid change in the DC level of the signal. Therefore, in order to avoid such generation of noise, it has been necessary for prior art receivers, like the generic one described above, to remain active for a certain period of time after the last wanted data symbol. By doing so, the digital filters are fed with a signal with essentially nonvarying DC-level for as long as it takes for the last symbol to pass through the digital filters. Obviously, this contradicts the above objective of allowing an immediate switch to a passive mode or transmit mode.
THE INVENTION
Therefore, it is an objective of the present invention to overcome the drawbacks of the prior art approach set out above. In particular, the purpose of the invention is to provide an improved communication signal receiver of the type having a plurality of components arranged along at least one signal path, the components along the or each signal path comprising a filter for processing a received signal and averaging means for deriving a mean value of the signal, where the improvements particularly lie in a more rapid switch from active to passive mode and reduced power consumption.
These objectives are achieved by connecting an output of the averaging means to a component located prior to the filter along the signal path, so that a mean value (or DC level) of the signal may be selectively fed back to the filter for a period of time immediately following the sampling of the last wanted data symbol. Since the filter will be supplied with a signal with no rapid change in DC level, the receiver circuits may be immediately switched off, after the last wanted data symbol has been sampled, without generating transient noise in the digital filter.
The objectives are also achieved by a method of operating the communication signal receiver, wherein a received signal is converted to a digital form and the signal is processed by at least one digital filter, by determining an average value of the signal, detecting an event in the signal, and in response thereof feeding the digital filter with the average value.
Other objectives, advantages and features of the present invention appear from the following detailed description, from the attached patent claims as well as from the drawings.


REFERENCES:
patent: 4101839 (1978-07-01), Poole et al.
patent: 4979230 (1990-12-01), Marz
patent: 5838735 (1998-11-01), Khullar
patent: 6081565 (2000-06-01), Marandi et al.
patent: 0 863 606 (1998-09-01), None
patent: 98/04050 (1998-01-01), None

Affiliated with

Also associated with

Rating

Communication signal receiver and an operating method therefor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Communication signal receiver and an operating method therefor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Communication signal receiver and an operating method therefor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3100605