Gain compression amplfier providing a linear compression function

• US 5,822,442 A
• Filed: 09/11/1995
• Issued: 10/13/1998
• Est. Priority Date: 09/11/1995
• Status: Expired due to Term

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Starkey Labs Incorporated
• Inventors: Agnew, Jeremy A., Wahl, Jerry R.
• Primary Examiner(s): CHIN, VIVIAN C
• Application Number:
  US08/526,806
• Time in Patent Office: 1,128 Days
• Field of Search: 381/106, 381/107, 381/108, 381/68.2, 381/68.4, 381/120, 333/14, 341/139, 330/278, 330/254, 330/260, 330/261, 455/72
• US Class Current: 381/107
• CPC Class Codes: H03G 7/08 incorporating negative feedback
• CPC Class Codes: H04R 25/356 Amplitude, e.g. amplitude shift or compression
• CPC Class Codes: H04R 25/502 using analog signal processing

Abstract

An amplifier uses gain compression techniques to provide linear gain control over a wide dynamic range, and includes an amplifier having input and output legs, a gain controller coupled between the input and output legs of the amplifier, a gain control circuit having an input coupled to the amplifier output leg and output coupled to the gain controller. The gain controller is responsive to a gain control signal to permit continuous gain adjustment of the amplifier. The gain control circuit is configured to compare an output voltage on the amplifier output leg with a predetermined threshold voltage and to generate a gain control signal on the gain control circuit output so as to provide continuous gain adjustment of the amplifier at least when the amplifier output voltage is greater than the threshold voltage. A hearing aid using a single compression amplifier or multiple compression amplifiers to minimize sound distortion and enhance user comfort is also provided.

Claims

1. A compression amplifier having a wide dynamic range and configured to provide independent compression control, which comprises:

an amplifier having an input and an output;

a gain controller coupled between said input and output of said amplifier, said gain controller being responsive to a gain control signal for providing continuous gain adjustment of said amplifier; and

a gain control circuit having an input coupled to said amplifier output and output coupled to said gain controller for comparing an output signal level on said amplifier output with a predetermined threshold signal level and for generating said gain control signal at said gain control circuit output so as to provide continuous gain adjustment of said amplifier at least when said amplifier output signal level is greater than said threshold signal level, wherein said gain control circuit includes;

a rectifier circuit portion having an input coupled to said output of said amplifier and an output, said output of said rectifier circuit portion providing a rectified signal;

a signal comparing circuit portion that receives said rectified signal and said predetermined threshold signal and generates an output signal which is the difference between said rectified signal level and said predetermined threshold signal level;

a summing circuit portion having a first input coupled to said output of said signal comparing circuit portion and a second input coupled to a sub-threshold amplifier, said summing circuit portion generates an output signal that is the sum of the signals on said first and second inputs; and

a signal generating circuit portion having an input coupled to said output of said summing circuit and an output coupled to said gain controller, said signal generating circuit portion continuously generates said gain control signal that is proportional to said rectified signal level and said predetermined threshold signal level.

2. The compression amplifier according to claim 1, wherein said gain control circuit includes means for selectively controlling said gain control signal such that when said output signal level on said amplifier output exceeds said predetermined threshold signal level said gain control signal is generated at said gain control circuit output.

3. The compression amplifier according to claim 2, wherein said selective controlling means comprises a relay switch.

4. The compression amplifier according to claim 1, wherein said predetermined threshold signal level for said compression amplifier is a voltage set to a value below a voltage where said amplifier saturates.

5. The compression amplifier according to claim 4, wherein said predetermined threshold voltage ranges from between about 7.8 mV (rms) and about 880 mV (rms).

6. The compression amplifier according to claim 1, wherein said amplifier comprises an operational amplifier having a fixed resistor connected to an input of said operational amplifier.

7. The compression amplifier according to claim 1, wherein said gain controller comprises a current-controlled resistor.

8. The compression amplifier according to claim 1 further comprising a switch connected between said output of said voltage comparing circuit portion and said first input of said summing circuit portion, said switch being responsive to a mode select signal derived from a comparison of said rectified signal level and said predetermined threshold signal level such that when said rectified signal level exceeds said predetermined threshold signal level said switch is activated.

9. A compression amplifier having a wide dynamic range and configured to provide selective gain compression, comprising:

an amplifier having an input and an output;

a gain control circuit having an input coupled to said amplifier output and an output, said gain control circuit being responsive to an output signal on said amplifier output and to a predetermined threshold signal for generating an output gain control current; and

a current controlled gain controller having a first input connected to said amplifier output, a second input connected to said gain control circuit output, and an output connected to said amplifier input, said gain controller being responsive to said gain control current such that when said gain control current changes said gain controller adjusts the gain of said amplifier;

wherein said gain control current is defined by;

##EQU15## and wherein said gain control circuit includes;

a rectifier circuit portion having an input coupled to said output of said amplifier and an output, said output of said rectifier circuit portion providing a rectified DC signal;

a signal comparing circuit portion receiving said rectified DC signal and said predetermined threshold signal for generating an output signal that is a difference between said rectified DC signal and said predetermined threshold signal;

a summing circuit portion having a first input coupled to said output of said signal comparing circuit portion and a second input coupled to a sub-threshold amplifier, said summing circuit portion generating an output signal that is a sum of the signals on said first and second inputs; and

a current generating circuit portion having an input coupled to said output of said summing circuit and an output coupled to said gain controller, said current generating circuit portion generating said gain control current which is proportional to said rectified DC signal and said predetermined threshold signal.

10. The compression amplifier according to claim 9, wherein said predetermined threshold signal for said compression amplifier is a voltage set to a value below a voltage where said amplifier saturates.

11. The compression amplifier according to claim 10, wherein said predetermined threshold voltage ranges from between about 7.8 mV (rms) and about 880 mV (rms).

12. A hearing aid comprising:

a preamplifier network having an input connected to a sound detector and an output, wherein said preamplifier network includes a compression amplifier having an amplifier with an input leg and an output leg corresponding to said output of said preamplifier network, a gain controller coupled between said input and output legs of said amplifier, said gain controller being responsive to a gain control signal to permit continuous gain adjustment of said amplifier, and a gain control circuit having an input coupled to said amplifier output and output coupled to said gain controller, said gain control circuit for comparing an output voltage on said amplifier output with a predetermined threshold signal and for generating said gain control signal on said gain control circuit output so as to provide continuous gain adjustment of said amplifier at least when said amplifier output signal is greater than said predetermined threshold signal; and

an output drive network having an input connected to said output of said preamplifier network and an output connected to a sound transducer, said output drive network including an amplifier having a fixed gain, wherein said preamplifier network gain control circuit includes;

a rectifier circuit portion having an input coupled to said output of said amplifier and an output, said output of said rectifier circuit portion providing a rectified voltage;

a voltage comparing circuit portion receiving said rectified voltage and said predetermined threshold voltage and generating an output signal that is a difference between said rectified voltage and said predetermined threshold voltage;

a summing circuit portion having a first input coupled to said output of said voltage comparing circuit portion and a second input coupled to a sub-threshold amplifier, said summing circuit portion generating an output signal that is a sum of the signals on said first and second inputs; and

a current generating circuit portion having an input coupled to said output of said summing circuit and an output coupled to said gain controller, said current generating circuit generating a gain control current that is proportional to said rectified voltage and said predetermined threshold voltage.

13. The hearing aid according to claim 12, wherein said predetermined threshold signal for said hearing aid is a voltage set to a value below a voltage where said preamplifier network amplifier saturates.

14. The hearing aid according to claim 13, wherein said predetermined threshold voltage ranges from between about 7.8 mV (rms) and about 880 mV (rms).

15. The hearing aid according to claim 12, wherein said gain control current is defined by:

##EQU16##

16. The hearing aid according to claim 12, wherein said gain control circuit includes means for selectively controlling said gain control signal such that when a signal level on said amplifier output exceeds a signal level of said predetermined threshold signal said gain control signal is generated on said gain control circuit output.

17. A hearing aid comprising:

a preamplifier network having an input connected to a sound detector and an output; and

an output drive network having an input connected to said output of said preamplifier network and an output connected to a sound transducer, said output drive network including a compression amplifier having an amplifier with an input leg and an output leg corresponding to said output drive network output, a gain controller coupled between said input and output legs of said output drive network amplifier, said gain controller being responsive to a gain control signal for providing continuous gain adjustment of said output drive network amplifier, and a gain control circuit having an input coupled to said output drive amplifier output and output coupled to said gain controlling device, said gain control circuit for comparing an output voltage on said output drive network amplifier output with a predetermined threshold signal and for generating said gain control signal on said gain control circuit output so as to provide continuous gain adjustment of said output network amplifier at least when said output drive network amplifier output signal is greater than said predetermined threshold signal, wherein said output drive network gain control circuit includes;

a rectifier circuit portion having an input coupled to said output of said output drive network amplifier and an output, said output of said rectifier circuit portion providing a rectified voltage;

a voltage comparing circuit portion receiving said rectified voltage and said predetermined threshold voltage and generating an output signal that is a difference between said rectified voltage and said predetermined threshold voltage;

a summing circuit portion having a first input coupled to said output of said voltage comparing circuit portion and a second input coupled to a sub-threshold amplifier, said summing circuit portion generating an output signal that is a sum of the signals on said first and second inputs; and

a current generating circuit portion having an input coupled to said output of said summing circuit and an output coupled to said gain controller, said current generating circuit generating a gain control current that is proportional to said rectified voltage and said predetermined threshold voltage.

18. The hearing aid according to claim 17, wherein said predetermined threshold signal for said hearing aid is a voltage set to a value below a voltage where said preamplifier network amplifier saturates.

19. The hearing aid according to claim 18, wherein said predetermined threshold voltage ranges from between about 7.8 mV (rms) and about 880 mV (rms).

20. The hearing aid according to claim 17, wherein said gain control current is defined by:

##EQU17##

21. The hearing aid according to claim 20, wherein said gain control current is about 1 μ

A.

22. The hearing aid according to claim 17, wherein said gain control circuit includes means for selectively controlling said gain control signal such that when a signal level on said amplifier output exceeds a predetermined threshold signal level said gain control signal is generated on said gain control circuit output.