Method and apparatus for synchronous demodulation of multiply modulated signals

An apparatus to synchronously demodulate a multiply modulated rotation rate signal of a rotation rate sensor, the apparatus comprising:

• a spring-mass system that oscillates at its natural resonant frequency;
• and
• at least one capacitor to ascertain a rotation rate of a Coriolis effect acting on the spring-mass system;
• a generating arrangement to generate a time-variable first electrical signal so that it exhibits a time-invariant phase relationship to the natural resonant frequency of the rotation rate sensor;
• a superimposing arrangement to superimpose a second electrical signal, at the natural resonant frequency of the rotation rate sensor, on the first electrical signal to provide a multiply modulated electrical signal, an amplitude of the second electrical signal of a time-variable capacitance change of the at least one capacitor being correspondingly modulated;
• and
• an ascertaining arrangement to ascertain the time-variable capacitance change associated with the rotation rate and ascertaining the rotation rate by multiply demodulating a multiply modulated electric signal;
• wherein:
• the at least one capacitor includes two stationary capacitor electrodes and a capacitor electrode that is movable as a consequence of the action of the rotation rate;
• the capacitor electrode is movable toward a first one of the two stationary capacitor electrodes and simultaneously movable away from a second one of the two stationary capacitor electrodes, the moving of the capacitor electrode bringing about two time-variable and mutually inverse capacitance changes;
• the second electrical signal superimposed on the first electrical signal is modulated in accordance with the two time-variable and mutually inverse capacitance changes;
• and
• the multiply modulated electrical signal is conveyed to a capacitance/voltage converter that delivers two mutually inverse time-variable voltage signals;
• wherein a first mutually inverse time-variable voltage signal is conveyed to a first input of a summer under a control of a first control signal, and a second mutually inverse time-variable voltage signal is conveyed to a second input of the summer under the control of the first control signal.