GB2377848A - Wheatstone bridge microphone circuit - Google Patents

Wheatstone bridge microphone circuit Download PDF

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Publication number
GB2377848A
GB2377848A GB0117743A GB0117743A GB2377848A GB 2377848 A GB2377848 A GB 2377848A GB 0117743 A GB0117743 A GB 0117743A GB 0117743 A GB0117743 A GB 0117743A GB 2377848 A GB2377848 A GB 2377848A
Authority
GB
United Kingdom
Prior art keywords
circuit
transducer
bridge
arms
differential amplifier
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB0117743A
Other versions
GB0117743D0 (en
GB2377848B (en
Inventor
Andrew Michael Wilkes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NEC Technologies UK Ltd
Original Assignee
NEC Technologies UK Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by NEC Technologies UK Ltd filed Critical NEC Technologies UK Ltd
Priority to GB0117743A priority Critical patent/GB2377848B/en
Publication of GB0117743D0 publication Critical patent/GB0117743D0/en
Publication of GB2377848A publication Critical patent/GB2377848A/en
Application granted granted Critical
Publication of GB2377848B publication Critical patent/GB2377848B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00Circuits for transducers, loudspeakers or microphones

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)

Abstract

A transducer circuit is described in which an electret condenser microphone 5 is included in one arm of a bridge circuit and a noise signal appearing in the Wheatstone bridge circuit with a bias voltage 7 is balanced out as a result of the application of outputs from the bridge circuit to a differential amplifier 9. The circuit may contain a reactive element in one arm of the bridge to balance the impedance of the transducer 5.

Description

<Desc/Clms Page number 1>
TRANSDUCER CIRCUIT This invention relates to a transducer circuit.
A transducer circuit in the form of a microphone circuit to be described below, by way of example in illustration of the present invention, minimises the effect of noise in a comparatively simple way. The circuit, in the example, employs an electret condenser microphone in one limb of a Wheatstone bridge, in which each arm of the bridge has substantially the same value. The transducer circuit may convert other signals than sound to electrical signals. For example, the transducer may be an optical coupler transducing light, or a strain gauge producing an electrical signal in response to a physical movement.
A circuit arrangement will now be described, by way of example, in the belief that it will enable the invention to be understood, with reference to the single figure of the accompanying drawing.
Referring to the Figure, there is shown a bridge circuit having a respective resistor of value R and labelled 1,2, 3 and 4 in each arm of the bridge. The resistor 4 is constituted by the inherent resistance value of a transducer in the form of an electret condenser microphone, which is indicated at 5, which includes a capacitive element and which provides a wanted signal Vs, as indicated at 6. A d. c. power supply 7 which is connected from a node formed by a junction a between the resistors 1 and 2
<Desc/Clms Page number 2>
to a node formed by a junction b between the microphone 5 and the resistor 3 provides a d. c. bias current to the microphone 5. It is the case that noise, indicated at 8 by Vn, is liable to appear in the microphone circuit, generally having been introduced via the power supply line associated with the power supply 7, and this noise is applied, in the particular circuit being described, to a differential amplifier, such as that shown at 9 to provide an output. The amplifier 9 is connected from the junction c between the resistor 4 and the resistor 1 to the junction d between the resistor 3 and the resistor 2.
The bridge in this arrangement provides signal inputs to the differential amplifier 9 in which the noise Vn is attenuated, or nullified.
If necessary, a capacitor 11 having a value C may be introduced, as indicated by the dotted lines across the resistor 3, in order to balance the effect of the capacitance of the microphone 5. Furthermore, the resistors 2, 3 and 4 may be replaced by impedances of corresponding value to that of the microphone 5.
Considering the operation of the circuit shown in the Figure, a first potential divider connected across the bias voltage supply 7 between the nodes a and b is formed by the resistor 1 in series with the microphone 5, and the microphone 5 is referenced to zero volts. The microphone 5 is thus d. c. biased, and the microphone signal Vs is output from the first potential divider, plus any power supply noise Vn indicated at 8.
A second potential divider, which is also connected between the nodes a and b across the bias voltage supply 7, is formed by the resistors 2 and 3. As has been explained, the resistors 1,2 and 3 have the same value
<Desc/Clms Page number 3>
of resistance as the nominal resistance value 4 of the microphone 5. The output from the second potential divider at the node d will include the power supply noise Vn with an equal amplitude and phase to that of the noise Vn which is included at the node c in the output from the first potential divider.
By the application of the outputs at c and d from the first and second potential dividers to the respective inputs of the differential amplifier 9, it is possible to obtain an output from the differential amplifier 9 from which the unwanted noise component Vn included in the two inputs has been cancelled. The output from the amplifier 9 is thus restricted to the wanted microphone signal Vs.
It will be understood that, in practice, it may not be possible to obtain the complete elimination of the unwanted noise, due to the difficulty in obtaining an exact match between the impedances of the microphone and those of the resistors 1,2 and 3. However, considerable degrees of attenuation of the noise Vn are possible.
It will be appreciated that, although a particular arrangement has been described, by way of example, in order to enable the invention to be understood, variations and modification thereof as well as other arrangements may be conceived within the scope of the appended claims.
For example, other forms of bridge may be employed, as may other forms of cancellation circuit than an amplifier having a differential input.
It would also be possible for the bridge to be inverted with the transducer represented by the microphone 5 and the balancing resistor or impedance 3 referenced to the positive supply rail a. Furthermore, any
<Desc/Clms Page number 4>
impedance of the transducer 5 may be balanced by a reactive element in one arm of the bridge.
It will be noted that the transducer generator, represented by the microphone 5, is in one arm of the bridge rather than across the voltage supply 7. It will also be appreciated that, although in the particular arrangement described by way of example, a Wheatstone bridge is employed, other well known forms of bridge circuit may be employed.

Claims (5)

1. A transducer circuit including a bridge circuit, the bridge circuit having first and second pairs of arms connected across first and second nodes, one of the first pair of arms including a transducer, first and second potential divider outputs being provided respectively at the junction between the first pair of arms and the junction between the second pair of arms, and a differential amplifier having first and second inputs, the first and second potential divider outputs being connected to the first and second inputs of the differential amplifier respectively.
2. A circuit as claimed in claim 1 in which the bridge circuit is a Wheatstone bridge.
3. A circuit as claimed in either claim 1 or claim 2 including a reactive element in one arm of the bridge to balance the impedance of the transducer.
4. A circuit as claimed in any one of the preceding claims in which the transducer is an electret condenser microphone.
5. A circuit as claimed in claim 1 including an arrangement substantially as described herein with reference to the single figure of the accompanying drawings.
5. A circuit as claimed in claim 1 including an arrangement substantially as described herein with reference to the single figure of the accompanying drawing.
<Desc/Clms Page number 6>
Amendments to the claims have been filed as follows CLAIMS
1. A transducer circuit including a bridge circuit, the bridge circuit having first and second pairs of arms connected across first and second nodes, one of the first pair of arms including a transducer, d. c. supply means arranged to provide a d. c. bias current to the transducer, first and second potential divider outputs being provided respectively at the junction between the first pair of arms and the junction between the second pairs of arms, a differential amplifier having first and second inputs, wherein the first and second potential divider outputs are connected to the first and second inputs of the differential amplifier respectively, and wherein the d. c. supply means is connected across the said first and second nodes of the bridge circuit.
2. A circuit as claimed in claim 1 in which the bridge circuit is a Wheatstone bridge.
3. A circuit as claimed in either claim 1 or claim 2 including a reactive element in one arm of the bridge to balance the impedance of the transducer.
4. A circuit as claimed in any one of the preceding claims in which the transducer is an electret condenser microphone.
GB0117743A 2001-07-20 2001-07-20 Transducer circuit Expired - Fee Related GB2377848B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0117743A GB2377848B (en) 2001-07-20 2001-07-20 Transducer circuit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0117743A GB2377848B (en) 2001-07-20 2001-07-20 Transducer circuit

Publications (3)

Publication Number Publication Date
GB0117743D0 GB0117743D0 (en) 2001-09-12
GB2377848A true GB2377848A (en) 2003-01-22
GB2377848B GB2377848B (en) 2004-08-11

Family

ID=9918896

Family Applications (1)

Application Number Title Priority Date Filing Date
GB0117743A Expired - Fee Related GB2377848B (en) 2001-07-20 2001-07-20 Transducer circuit

Country Status (1)

Country Link
GB (1) GB2377848B (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008045985A2 (en) * 2006-10-11 2008-04-17 Analog Devices, Inc. Microphone microchip device with differential mode noise suppression
WO2012163379A1 (en) * 2011-05-30 2012-12-06 Sony Ericsson Mobile Communications Ab Circuit assembly for processing an electrical signal of a microphone

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3766319A (en) * 1972-02-22 1973-10-16 E Gschwandtner Transducer circuit for simultaneous two way operation
DE3402282A1 (en) * 1984-01-24 1985-08-01 Hagenuk GmbH, 2300 Kiel Circuit arrangement for a telephone subscriber station
US4718083A (en) * 1985-09-23 1988-01-05 Gte Communication Systems Corporation Differential receive booster amplifier for telephone instruments
EP0732601A1 (en) * 1995-03-14 1996-09-18 Tda Armements S.A.S. Standby sensor with long autonomy
US5631602A (en) * 1995-08-07 1997-05-20 Delco Electronics Corporation Wheatstone bridge amplifier circuit with integrated diagnostic testing
WO2001036924A1 (en) * 1999-11-17 2001-05-25 Sieco, Inc. Torque compensated weight sensing modules

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3766319A (en) * 1972-02-22 1973-10-16 E Gschwandtner Transducer circuit for simultaneous two way operation
DE3402282A1 (en) * 1984-01-24 1985-08-01 Hagenuk GmbH, 2300 Kiel Circuit arrangement for a telephone subscriber station
US4718083A (en) * 1985-09-23 1988-01-05 Gte Communication Systems Corporation Differential receive booster amplifier for telephone instruments
EP0732601A1 (en) * 1995-03-14 1996-09-18 Tda Armements S.A.S. Standby sensor with long autonomy
US5631602A (en) * 1995-08-07 1997-05-20 Delco Electronics Corporation Wheatstone bridge amplifier circuit with integrated diagnostic testing
WO2001036924A1 (en) * 1999-11-17 2001-05-25 Sieco, Inc. Torque compensated weight sensing modules

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008045985A2 (en) * 2006-10-11 2008-04-17 Analog Devices, Inc. Microphone microchip device with differential mode noise suppression
WO2008045985A3 (en) * 2006-10-11 2008-05-29 Analog Devices Inc Microphone microchip device with differential mode noise suppression
WO2012163379A1 (en) * 2011-05-30 2012-12-06 Sony Ericsson Mobile Communications Ab Circuit assembly for processing an electrical signal of a microphone
US9077342B2 (en) 2011-05-30 2015-07-07 Sony Corporation Circuit assembly for processing an electrical signal of a microphone
US9407256B2 (en) 2011-05-30 2016-08-02 Sony Corporation Reducing a disturbance on a signal path of a semiconductor switch

Also Published As

Publication number Publication date
GB0117743D0 (en) 2001-09-12
GB2377848B (en) 2004-08-11

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Legal Events

Date Code Title Description
732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee

Effective date: 20060720