Frequency-stabilized two-state modulation using hysteresis control

An amplifier comprising,

• a two-state modulation system having an input terminal for receiving a signal to be amplified, an output terminal, closed loop means comprising apparatus for intercoupling said input terminal and said output terminal and having a two-state power processor for providing first and second signal amplitudes to said output terminal at a switching frequency corresponding to that of a driving signal provided by hysteretic means for providing said driving signal in response to a switching signal provided by first means for combining and related to the signal on said input terminal combined with a feedback signal coupled from said two-state power processor, said hysteretic means being characterized by a hysteresis loop representing the relationship between the input and output of said hysteretic means,
• hysteretic comparator means including said hysteretic means having first and second variable threshold levels d.sub.1 and d.sub.2 for switching in response to said switching signal,
• a source of a hysteresis control signal,
• means for coupling said source of a hysteresis control signal to said hysteretic means to establish said first and second variable threshold levels and control said hysteresis loop to maintain said switching frequency substantially constant in the presence of variations in the ratio of time the output signal is said first amplitude relative to time said output signal is said second amplitude which ratio is representative of the signal on said input terminal,
• an averaging circuit having an input coupled to said output terminal and a signal output for providing as an output signal the signal on said input terminal amplified,
• a source of a dither signal for dithering the frequency of said switching signal,
• and means for coupling said dither signal to said hysteretic means as at least a component of said hysteresis control signal.