Apparatus for producing a radio-frequency signal

Details Apparatus for producing a radio-frequency signal Apparatus for producing a radio-frequency signal

2000-05-09

2003-10-07

Bost, Dwayne (Department: 2681)

Telecommunications

Transmitter

C455S108000, C455S118000, C375S295000

Reexamination Certificate

active

06631254

ABSTRACT:

The present invention relates to apparatus for producing a radio frequency signal with non-constant envelope modulation.
So-called “Cartesian” amplifiers have been used in radio equipment for use, for example, in mobile radio systems. In a Cartesian amplifier, a base band signal resolved into I and Q quadrature components which are processed separately for modulation purposes and recombined just prior to application to the radio frequency amplifier. These amplifiers are subject to two limitations, namely they are capable of handling only a relatively narrow bandwidth at baseband (e.g. up to 25 KHz), and there is a noise floor which it is not possible to remove due to the action of the feedback loop and the use of a vector modulator.
The present invention seeks to provide an apparatus which can produce a non-constant-envelope radio frequency output signal with a transmission bandwidth greater than a Cartesian amplifier, e.g. of the order of a few hundred kiloherz, and which is capable of low noise performance.
According to the present invention there is provided an apparatus for producing a non-constant-envelope radio frequency signal comprising:
a) an input for a baseband signal;
b) means for generating from the baseband signal a modulated radio frequency signal of substantially constant envelope amplitude and suitable for radio-frequency amplification to a level for broadcasting;
c) means for envelope-modulating and outputting the amplified radio-frequency modulated signal so as to have a required non-constant envelope;
wherein
the generating means b) comprises i) a frequency-offset phase locked loop including a frequency-controllable oscillator which produces as its output said modulated radio frequency signal of substantially constant envelope amplitude and ii) a phase comparator, the output of the phase comparator being a signal representing the phase difference between a constant-envelope-amplitude signal derived from the output of means c) and a constant-envelope signal derived from the baseband signal.


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European Search Report dated Sep. 2000, 3 pages.
Search Report Under Section 17(5) dated Jul. 30, 1999 (2 pages).

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