Adaptive power line noise filter and switch for audio reproduction equipment

• US 5,043,686 A
• Filed: 03/14/1989
• Issued: 08/27/1991
• Est. Priority Date: 03/14/1989
• Status: Expired due to Term

• Current Assignee: Harman Electronics Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Inventors: Plunkett, Bradley J.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/324,006
• Time in Patent Office: 896 Days
• Field of Search: 333/12, 333/17.1, 333/18, 333/101, 333/181, 333/262, 381/94, 381/93, 323/286, 363/39, 363/44, 363/45, 363/89, 328/520
• US Class Current: 333/181
• CPC Class Codes: H03H 21/0001 Analogue adaptive filters

Abstract

A filter circuit for reducing power line noise to audio reproduction equipment. Audio reproduction equipment requires a power source without excessive line noise; however, power sources, particularly in the automotive environment, often generate a substantial amount of noise which can degrade audio reproduction quality. The present invention utilizes a filter circuit which regulates and smooths the power in line between the power source and the audio equipment. The regulation and degree of filtering is further controlled by feedback from the power output and/or from the audio output to provide a sufficient quantity of filtering at various audio levels without affecting the power transmission to the audio equipment through excessive power loss. The power output after filtering is sampled and compared to a reference voltage to create an error signal. The degree of filtering is then adjusted in response to the value of the error signal to provide appropriate filtering without excessive power loss. The audio feedback is utilized to regulate the amount of filtering to decrease the filtering and decrease the voltage loss during high audio output, and to increase filtering during low audio output to provide the necessary line noise conditioning for various audio conditions.

Claims

1. An adaptive power line filter for an audio reproduction system, comprising:

an input port which may be operably connected to a power line in order to accept an input voltage;

an output port for outputting an output voltage to a load;

a variable conductivity element interposed between said input and output ports, wherein the conductivity of said conductivity element varies in accordance with a voltage applied to a gate of said conductivity element;

a filter network for filtering the input voltage and applying the filtered voltage to the gate of said conductivity element so that the output voltage is a filtered version of the input voltage; and

,

a feedback network for producing a control signal in accordance with the difference between the output voltage level and a predetermined reference voltage level, the control signal then being applied to the gate of said conductivity element so that the input voltage is filtered less as the output voltage level increases.

2. The invention as recited in claim 1, wherein said variable conductivity element comprises an MOS field effect transistor.

3. The invention as recited in claim 1, wherein said feedback network comprises a comparator coupled to the output voltage of said output port for comparing the same to a reference signal.

4. The invention as recited in claim 3, wherein said feedback network further comprises a variable charge pump multiplier responsive to the output of the comparator for producing said control signal, said variable charge pump multiplier including a variable frequency oscillator.

5. The invention as recited in claim 4, wherein said feedback network further comprises a circuit adding a signal representative of the output of the audio reproduction system to the output of the comparator.

6. The invention as recited in claim 3, wherein said feedback network further comprises a means for coupling the output of the comparator to the gate of said MOS field effect transistor.

7. An adaptive power line filter for an audio reproduction system, comprising:

a first circuit for accepting a power input from a power line and outputting a filtered power output wherein a variable degree of line filtering is provided in response to a control signal; and

a second circuit for generating said control signal in response to the voltage drop across said first circuit between the power input and the power output and an output of the audio reproduction system, whereby efficient line filtering is provided at low audio output levels and losses associated with line filtering are reduced at high audio output levels without perceptible degradation of audio fidelity.

8. The invention as recited in claim 7, wherein said first circuit includes a filter network and a variable transconductance semiconductor.

9. The invention as recited in claim 7, wherein said second circuit includes a reference signal and a comparator for comparing the output of the first circuit with said reference signal.

10. The invention as recited in claim 9, wherein the second circuit further includes an oscillator having an output signal the frequency of which varies in response to the output of the comparator.

11. The invention as recited in claim 8, wherein said second circuit comprises a differential amplifier for comparing the output of said first circuit with a predetermined reference voltage and an oscillator for producing said control signal in accordance with the output of said differential amplifier.

12. An adaptive power line noise filter, comprising:

a power input;

a power output;

a filter network coupled between said power input and said power output, said filter network providing a variable degree of transconductance therethrough in response to a variable control signal;

a comparator coupled to said power output for sampling said power output, comparing said sampled output to a reference and producing a sampling signal indicative of said comparison; and

a compensator connected to said filter network and said comparator for receiving said sampling signal and generating said variable control signal in response to said sampling signal.

13. The filter of claim 12, wherein said compensator includes a variable frequency oscillator.

14. The filter of claim 12, further comprising a switch network for disabling said filter network.

15. The filter of claim 12, further comprising a circuit for measuring a level of an audio output of a unit of audio reproduction equipment and for modifying said variable control signal in response to said measured audio output level.

16. The filter of claim 12, wherein said filter network includes an MOS field effect transistor.