The present invention, generally speaking, provides methods and apparatus for
producing an amplitude modulated communications signal, in which a constant-envelope
carrier signal is modified in response to a power control signal to produce a modified
constant-envelope carrier signal. The modified constant-envelope carrier signal
is amplified in response to an amplitude modulation signal to produce a communications
signal having amplitude modulation and having an average output power proportional
to a signal level of the modified constant-envelope carrier signal. This manner
of operation allows wide dynamic range of average output power to be achieved.
Because amplitude modulation is applied after amplitude varying circuitry used
to produce the modified constant-envelope carrier signal, the amplitude modulation
is unaffected by possible non-linearities of such circuitry. In accordance with
another aspect of the invention, operation in the foregoing manner at comparatively
low average output power levels is combined with switch mode operation at comparatively
high average output power levels, enabling high overall efficiency to be achieved.
Hence, the disclosed modulator and amplifier combination, in addition to supporting
very low power signals, also supports high power signals.