Telecommunications – Transmitter – With feedback of modulated output signal
Reexamination Certificate
1997-09-26
2001-04-10
Eisenzopf, Reinhard J. (Department: 2682)
Telecommunications
Transmitter
With feedback of modulated output signal
C455S116000
Reexamination Certificate
active
06215986
ABSTRACT:
TECHNICAL FIELD
This invention relates to wireless communication systems, particularly to radio transmitters.
TECHNICAL BACKGROUND
It is of general interest and concern to reduce distortion in radio frequency communication, which is usually in channels as close together in frequency as practicable in order to maximize use of radio frequency spectrum available to communications concerned. Non-linearity in transmitter mixer and output amplifier stages operative for one channel can lead to unwanted emissions in nearby channels. Many techniques of considerable sophistication have been used or proposed for use in reducing distortion. Such techniques include separate processing of in-phase and quadrature phase components (I/Q) of normally analogue RF signals, and digital signal processing (DSP) in which analogue RF signals are passed through an analogue-to-digital converter for processing digitally in special-purpose logic hardware or program-controlled processing or arithmetic unit with results often converted back from digital to analogue form. Both of I/Q and DSP techniques have inherent capability to correct both amplitude and phase errors. However, they tend to be rather complex and directed at particular radio communication systems, also quite costly to implement.
SUMMARY OF THE INVENTION
It is an object of this invention to provide simpler and less costly distortion reduction, preferably with application widely to amplitude modulation (AM), single side band (SSB) and multitone radio communication systems.
According to first system and method aspects of this invention utilize, relative to mixer and amplifier output stages receiving signals in modulated carrier form, negative feedback of detected RF output signal envelope to input of said mixer means of active type.
Direct to use of negative feedback of RF output envelope to final mixer and amplifier output stages in preferred embodiments of this invention is usefully effective in a simple and low-cost manner relative to correction of amplitude errors. Phase errors will, of course, not be corrected, but good practical utility is seen by way of reducing phase shift/stability problems for amplitude time-variable modulation systems including SSB and AM multitone types, actually aided by unprocessed state of the feedback signal in anti-phase but otherwise nominally identical with envelope of already carrier-modulated mixer input signal (for further carrier modulation fully to transmission form by the mixer).
It is to be understood and appreciated that proposed negative feedback of anti-phase RF envelope is applicable to mixer input whether from RF exciter stage or from first IF stage.
One known system, see European patent specification no 0441579, uses RF output signal envelope detection, but concentrates on SSB transmitters and phase error correction including zero-crossing problems; particularly further requiring RF input signal envelope detection and deriving envelope error signals for phase-lock loop control, via a divider, of phase modulators for both of input and feedback signals. Interestingly, its indicated associated provision for amplitude error correction is as in UK patent specification no 2 240 892, which also requires deriving input and output envelope error signals used via a divider to modulate both of input and feedback signals. These prior patent specifications represent an inherently different and much more complex approach to the present invention's concentration simply on amplitude error correction/control by direct application of negative feedback envelope signals.
Application of the invention is particularly convenient in the light of widespread use nowadays of integrated mixers generally of active type, for example of Gilbert cell architecture; and results in linearization of both such active mixer and associated output power amplifier together. Avoidance of any “summing” of audio/data input base band signals with demodulated and processed output signals to generate error signals is advantageous, perhaps particularly for SSB transmitters where successful such “summing” is far from straightforward.
Achievable linearization is of much wider bandwidth than existing linearization techniques (which tend to be quite narrow band), being limited only by time constraints and any loop filtering in the signal and/or feedback paths so that distortion (such as intermodulation products) is reduced over a wide band to either side of the transmitted signal.
REFERENCES:
patent: 4088956 (1978-05-01), Axman
patent: 4412337 (1983-10-01), Bickley et al.
patent: 5023937 (1991-06-01), Opas
patent: 5124665 (1992-06-01), McGann
patent: 5193223 (1993-03-01), Walczak et al.
patent: 5241687 (1993-08-01), Short
patent: 5423082 (1995-06-01), Cygan et al.
patent: 5430416 (1995-07-01), Black et al.
patent: 5535247 (1996-07-01), Galius et al.
patent: 5542096 (1996-07-01), Cygan et al.
patent: 5564087 (1996-10-01), Cygan et al.
patent: 5752171 (1998-05-01), Akiya
patent: 5793817 (1998-08-01), Wilson
patent: 0 441 579 A1 (1991-08-01), None
patent: 0441579 A1 (1991-08-01), None
patent: 728327 (1955-04-01), None
patent: 2 265 270 (1993-09-01), None
patent: 2 272 589 (1994-05-01), None
patent: 2 240 892 (1994-06-01), None
patent: 2240892 (1994-06-01), None
patent: 0 638 994 A1 (1995-02-01), None
patent: 2 281 668 (1995-03-01), None
patent: 2 283 628 (1995-05-01), None
patent: 2 287 371 (1995-09-01), None
patent: 2 301 247 (1996-11-01), None
patent: WO 92/20147 (1992-11-01), None
Bhattacharya Sam
Chapman and Cutler
Eisenzopf Reinhard J.
Nortel Networks Corporation
LandOfFree
Reducing radio transmitter distortion does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reducing radio transmitter distortion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reducing radio transmitter distortion will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2547362