Frequency-stabilized two-state modulation using hysteresis control

• US 5,345,165 A
• Filed: 08/15/1990
• Issued: 09/06/1994
• Est. Priority Date: 11/02/1984
• Status: Expired due to Term

• Current Assignee: Bose Corporation
• Original Assignee: Bose Corporation
• Inventors: Froeschle, Thomas A.
• Primary Examiner(s): BEHA JR, WILLIAM
• Application Number:
  US07/568,532
• Time in Patent Office: 1,483 Days
• Field of Search: 323/222, 323/286, 323/267, 323/271, 323/284, 363/41, 363/21, 363/98, 330/10, 330/207 A , 330/251, 381/121
• US Class Current: 323/284
• CPC Class Codes: H03F 2200/351 Pulse width modulation being used in an amplifying circuit
• CPC Class Codes: H03F 2200/66 Clipping circuitry being present in an amplifier, i.e. the shape of the signal being modified
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers

Abstract

A two-state modulation system includes a hysteretic comparator with variable thresholds, a two-state processor and an integrating element. A summing circuit combines a signal coupled from the output of the two-state processor, the signal output, the signal input and a delay compensating signal feedback input and a feedback input from an integrating element at the output of the two-state processor. The hysteretic comparator receives a hysteresis control signal that varies the threshold. The hysteresis control signal may be provided by analog switches switched by the switching signal to provide the switched two-state levels to a low pass filter. Rectifying circuitry may also be used for supplying the hysteresis control signal. Limiters and compressors may be connected to the input with the limiter limiting levels tracking the two-state levels, and the compression proportional to the switching frequency.

Claims

1. 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 d₁ and d₂ 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.

2. In a two-state modulation system having an input terminal, 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, the improvement comprising,

hysteretic comparator means including said hysteretic means having first and second variable threshold levels d₁ and d₂ for switching in response to said switching signal,

a source of a hysteresis control signal,

and 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,

and further comprising 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.