Audio input circuit for voice recognition

• US 5,459,792 A
• Filed: 12/15/1993
• Issued: 10/17/1995
• Est. Priority Date: 12/15/1993
• Status: Expired due to Fees

• Current Assignee: Audio Technica U.S. Inc (Audio-Technica Corporation)
• Original Assignee: Audio Technica U.S. Inc (Audio-Technica Corporation)
• Inventors: Statham, Kelly, Reichel, Ken
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): Grant, II, Jerome
• Application Number:
  US08/168,047
• Time in Patent Office: 671 Days
• Field of Search: 381/56, 381/57, 381/111, 381/122, 381/112-115
• US Class Current: 381/111
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones

Abstract

An audio input circuit for providing a transducer output signal from a sound transducer to the input of a host device including a universal interface for coupling the transducer output signal to the host device. The universal interface includes a first signal input, a second signal input, a first output conductor, and a second output conductor. Additionally, the audio input circuit includes a switch mechanism coupled between the first and second signal input and between the first and second output conductors for selectively isolating the first output conductor from the second output conductor and for selectively coupling the first output conductor to the second output conductor. The audio input circuit conditions the output of an inexpensive microphone such that the output response of the microphone is ideally suited to the input requirements of the voice recognition host device.

Claims

1. An audio input circuit for providing a transducer output signal from a sound transducer to an input of a host device, comprising:

universal interface means for coupling the transducer output signal to the host device, said universal interface means having a first signal input, a second signal input, a first output conductor, and a second output conductor; and

switch means coupled between said first and second signal inputs and between said first and second output conductors for selectively isolating said first output conductor from said second output conductor and for selectively coupling said first output conductor to said second output conductor, said switch means comprising;

first selectable DC bias voltage blocking means for preventing a DC voltage present on said first output conductor from appearing on said first signal input.

2. The audio input circuit as defined in claim 1 wherein said switch means further comprises:

selectable AC coupling means for coupling at least one of said first signal input or said second signal input to a ground path.

3. The audio input circuit as defined in claim 2 wherein said selectable AC coupling means further comprises:

an AC coupling capacitive element; and

AC coupling switch means for coupling said capacitive element to a ground path.

4. The audio input circuit as defined in claim 1 wherein said first selectable DC bias voltage blocking means further comprises:

a first DC bias switch means in series with a parallel combination of a second DC bias switch means and a first capacitive element; and

said first and second DC bias switch means and capacitive element are coupled between said first signal input and said first output conductor.

5. The audio input circuit as defined in claim 1 wherein said first output conductor and said second output conductor are formed in a plug for connecting to the host device, said plug further comprising:

a shield output conductor for common connection between said plug an the host device.

6. The audio input circuit as defined in claim 1 further comprising:

an adjustable gain circuit for receiving the transducer output signal and having an adjustable gain output;

an amplifier circuit operatively coupled to receive said adjustable gain output to provide an amplified transducer output signal; and

filter means operatively coupled to said amplifier circuit for removing low frequency signals from said amplified transducer output signal.

7. The audio input circuit as defined in claim 6 wherein said filter means further comprises:

resistive, capacitive, and inductive elements configured as a tuned circuit and operatively coupled to said amplifier; and

a transformer having at least a portion of a primary winding forming said inductive element.

8. The audio input circuit as defined in claim 6 wherein said adjustable gain circuit further comprises:

a variable resistive element for providing an adjustable gain.

9. The audio input circuit as defined in claim 6 wherein said amplifier further comprises:

a transistor having an emitter, a base for receiving said adjustable gain output, and a collector for providing said amplified transducer output signal, said filter means operatively coupled between said base and said collector.

10. The audio input circuit as defined in claim 6 further comprising:

an internal electrical power source for optionally supplying power;

power sensing means for switchably providing electrical power from said internal power source or from an external power source; and

a transformer having a secondary winding, said secondary winding having a first terminal operatively coupled to said first signal input, a second terminal operatively coupled to said second signal input, and a third terminal operatively coupled to said external power source.

11. The audio input circuit as defined in claim 10 wherein said power sensing means decouples said internal power source when said external power source is beyond a predetermined threshold and is present on at least one of said first output conductor or said second output conductor, and said power sensing means couples said internal power source when said external power source is not present.

12. An audio input circuit for providing a transducer output signal from a sound transducer to an input of a host device, comprising:

universal interface means for coupling the transducer output signal to the host device, having a first signal input, a second signal input, a first output conductor, and a second output conductor;

first selectable DC bias voltage blocking means for preventing a DC voltage present on said first output conductor from appearing on aid first signal input;

an adjustable gain circuit for receiving the transducer output signal and having an adjustable gain output;

an amplifier circuit operatively coupled to receive said adjustable gain output to provide an amplified transducer output signal; and

filter means operatively coupled to said amplifier circuit for removing low frequency signals from said amplified transducer output signal, said filter means comprising;

resistive, capacitive, and inductive elements configured as a tuned circuit and operatively coupled to said amplifier; and

a transformer having at least a portion of a primary winding forming said inductive element.

13. The audio input circuit as defined in claim 12 further comprising:

selectable AC coupling means for coupling at least one of said first signal input or said second signal input to a ground path.

14. The audio input circuit as defined in claim 13 wherein said universal interface means further comprises:

second selectable DC bias voltage blocking means for preventing a DC voltage present on said second output conductor from appearing on said second signal input.

15. An audio input circuit for providing a transducer output signal from a sound transducer to an input of a host device, comprising:

(a) universal interface means for coupling the transducer output signal to the host device, having a first signal input, a second signal input, a first output conductor, and a second output conductor, said universal interface means having first selectable DC bias voltage blocking means for preventing a DC voltage present on said first output conductor from appearing on said first signal input, said first selectable DC bias voltage blocking means further including a first DC bias switch means in series with a parallel combination of a second DC bias switch means and a first capacitive element;

second selectable DC bias voltage blocking means for preventing a DC voltage present on said second output conductor from appearing on said second signal input, said second selectable DC bias voltage blocking means further including a third DC bias switch means in series with a parallel combination of a fourth DC bias switch means and a second capacitive element;

selectable AC coupling means for coupling at least one of said first signal input or said second signal input to an electrical return path;

(b) an adjustable gain circuit for receiving the transducer output signal and having an adjustable gain output;

(c) an amplifier circuit operatively coupled to receive said adjustable gain output to provide an amplified transducer output signal;

(d) filter means operatively coupled to said amplifier circuit for removing low frequency signals from said amplified transducer output signal; and

(e) wherein said first output conductor and said second output conductor are formed in a plug for connecting to the host device, said plug further including a shield output conductor for common connection between said plug an the host device.

16. The audio input circuit as defined in claim 15 further comprising:

a transformer having a secondary winding, said secondary winding having a first terminal operatively coupled to said first signal input, a second terminal operatively coupled to said second signal input, and a third terminal operatively coupled to said external power source; and

wherein first, second, third, and fourth DC bias switch means are dual-in-line package (DIP) switches.

17. An audio input circuit for providing a transducer output signal from a sound transducer to an input of a host device, comprising:

universal interface means for coupling the transducer output signal to the host device, said universal interface means having a first signal input, a second signal input, a first output conductor, and a second output conductor;

switch means coupled between said first and second signal inputs and between said first and second output conductors for selectively isolating said first output conductor from said second output conductor and for selectively coupling said first output conductor to said second output conductor, and an inductive element that couples said first signal input to said second signal input.