Multi-mode modulator and transmitter

A circuit for modulating an input signal x(t) to an output signal y(t), said circuit comprising:

• a first mixer having an input for an RF signal, an input for a first mixing signal f1 and an output for a mixed signal based on said two input signals;
• a second mixer having an input for an RF signal, an input for a second mixing signal f2 and an output for a mixed signal based on said two input signals, said output providing said output signal y(t), and said output of said first mixer being connected to said RF input of said second mixer;
• a switch having one input and two outputs, said input for receiving said input signal x(t) and said two outputs being connected to separate ones of said RF signal inputs of said first mixer and said second mixer, whereby said switch can be selectively controlled to direct said input signal x(t) to the input of either said first mixer or said second mixer;
• a first signal generator, for generating a multi-tonal mixing signal φ1 and providing said first mixing signal to said first mixer;
• a second signal generator, for generating a mono-tonal mixing signal φ2 and providing said second mixing signal to said second mixer;
• and
• a control circuit for controlling the position of said switch and the signals generated by said first signal generator and said second generator, said control circuit having two modes:
• a first mode in which said switch is positioned to feed said input signal x(t) to said second mixer, and said second signal generator is operable to generate a direct-conversion type oscillator signal;
• and
• a second mode in which said switch is positioned to feed said input signal x(t) to said first mixer, and said first and second signal generators are controlled to generate a virtual local oscillator signal pair where φ1*φ2 has significant power at the frequency of a local oscillator signal being emulated, and neither of said φ1 nor said φ2 having significant power at the frequency of said input signal x(t) or said LO signal being emulated.