Transmit modulation circuit and method of operating a transmitter

A transmit modulation circuit comprising:

• a fractional N synthesizer;
• a baseband digital modulation stage coupled to the fractional N synthesizer;
• a baseband I/Q modulation stage coupled to the fractional N synthesizer;
• the fractional N synthesizer and the baseband digital modulation stage implement a GMSK modulation mode;
• and
• the fractional N synthesizer and the baseband I/Q modulation stage implement a modulation mode selected from a group consisting of a m-16QAM modulation mode, a DQPSK modulation mode, and a narrow band frequency modulation mode.

A transmit modulation circuit comprising:

• a fractional N synthesizer;
• a baseband digital modulation stage coupled to the fractional N synthesizer,
• the baseband digital modulation stage comprising:
• a filter;
• a phase equalizer coupled to the filter;
• a digital-to-analog converter coupled to the phase equalizer;
• and
• an attenuator coupled to the digital-to-analog converter and to the filter;
• and
• a baseband I/Q modulation stage coupled to the fractional N synthesizer.

A transmit modulation circuit comprising:

• a fractional N synthesizer;
• a baseband digital modulation stage coupled to the fractional N synthesizer;
• and
• a baseband I/Q modulation stage coupled to the fractional N synthesizer,
• the baseband I/Q modulation stage comprising:
• a data interface;
• a data register coupled to the data interface;
• a first filter coupled to the data register;
• a second filter coupled to the data register;
• a first digital-to-analog converter coupled to the first filter;
• a second digital-to-analog converter coupled to the second filter;
• a third filter coupled to the first digital-to-analog converter;
• and
• a fourth filter coupled to the second digital-to-analog converter.

A portable transmitter comprising:

• a fractional N synthesizer;
• a baseband digital modulation stage coupled to the fractional N synthesizer;
• a baseband I/Q modulation stage coupled to the fractional N synthesizer;
• a first filtered amplifier stage coupled to the fractional N synthesizer;
• a second filtered amplifier stage coupled to the baseband I/Q modulation stage;
• a switched antenna filter network coupled to the first and second filtered amplifier stages;
• and
• a microcontroller coupled to the baseband digital modulation stage and the baseband I/Q modulation stage,
• wherein:
• the fractional N synthesizer operates with the baseband digital modulation stage in a first transmission mode;
• and
• the fractional N synthesizer operates with the baseband I/Q modulation stage in a second transmission mode different from the first transmission mode.