Digital modulator with digital power control circuit

In a digital modulator having digital multiplier means to which a digital modulating signal is applied, digital-to-analog (D/A) converter means coupled to the output of said digital multiplier means, and low-pass filter means connected to the output of said D/A converter means, a power control circuit comprising:

• means for deriving a digital power control signal from intensity of a signal received from a mobile station;
• a delay circuit for delaying the digital power control signal for a prescribed interval to produce a delayed version of the digital power control signal;
• and
• a memory storing digital values in locations addressable in response to a non-delayed version of said digital power control signal and in response to the delayed version of said digital power control signal to produce a digital multiplying signal which varies gradually during said prescribed interval when there is a difference in magnitude between said delayed and non-delayed versions of the power control signal, and applying said digital multiplying signal to said digital multiplier means so that said digital modulating signal is scaled with said digital multiplying signal.

In a mobile communication system having a base station and a plurality of mobile stations, said base station comprising:

• a power control circuit for receiving a signal from a mobile station and producing a digital power control signal representative of the power level of the received signal;
• first and second digital multipliers for multiplying digital signals having orthogonal phase relationships with said digital power control signal;
• first and second digital-to-analog converters for converting digital output signals from said first and second multipliers into analog signals;
• first and second low-pass filters connected to outputs of said digital-to-analog converters, respectively;
• orthogonal modulator means for mixing orthogonal phase carriers with output signals from said first and second low-pass filters to produce first and second orthogonally modulated signals and combining the modulated signals to produce a transmit signal;
• and
• constant-gain amplifier means for amplifying the transmit signal for transmission to said mobile station.