A transmitter includes a modulating and combining circuit to which signals are supplied and modulated into in-phase and quadrature-phase signals. The in-phase and quadrature-phase signals are combined in a closed-loop voltage summing circuit. The voltage summing circuit is an amplifier using capacitors as negative feedback elements. The negative feedback improves the linearity of the modulator. An LC tank circuit at the output of the voltage summing circuit bandpass filters the output before being applied to a power amplifier and eventually transmitted by an antenna. A multi-summing amplifier with different frequency tuning can be used for a multi-band transmitter design.