ELECTRONIC CIRCUIT FOR A MICROPHONE AND MICROPHONE

Abstract

The electronic circuit (10) comprises an input stage (Pre_amp) for pre-amplifying an electrical input signal of the electronic circuit (10) provided by a transducer (MEMS). Furthermore, the electronic circuit (10) comprises an output stage (T_amp) for providing a microphone output signal by processing an output signal of the input stage (Pre_amp). The electronic circuit (10) comprises an adjustable output load (RS) arranged and configured for setting a current draw of the output stage (T_amp). Additionally, the electronic circuit (10) comprises a measurement circuit (P_det) configured to capture the output signal of the input stage (Pre_amp) and an automatic control circuit (ACC) configured to adjust the adjustable output load (RS) dependent on the captured output signal of the input stage (Pre_amp).

Claims

1. An electronic circuit for a microphone, the electronic circuit comprising: an input stage for pre-amplifing an electrical input signal of the electronic circuit provided by a transducer, an output stage for providing an microphone output signal by processing an output signal of the input stage, an adjustable output load arranged and configured for setting a current draw of the output stage, a measurement circuit configured to capture an output signal of the input stage and an automatic control circuit configured to adjust the adjustable output load dependent on the captured output signal of the input stage.

2. The electronic circuit of claim 1, wherein the electronic circuit is operable in a two-terminal mode and comprises a first terminal configured for microphone output and power supply or ground.

3. The electronic circuit according to claim 1, wherein the electronic circuit comprises a second terminal for ground, a third terminal and a two-terminal mode configuration network coupled to the third terminal and/or coupled in parallel to the output load.

4. The electronic circuit of claim 3, wherein the two-terminal mode configuration network comprises at least one adjustable circuit element.

5. The electronic circuit according to claim 1, wherein a gain of the input stage is adjustable.

6. The electronic circuit according to claim 5, wherein the automatic control circuit is configured to adjust the gain of the input stage.

7. The electronic circuit according to claim 3, wherein the two-terminal mode configuration network comprises at least one adjustable on-chip resistor.

8. The electronic circuit according to claim 3, wherein the two-terminal mode configuration network comprises a first resistor arranged in parallel to a second resistor, wherein the first resistor is connectable in series with a capacitor.

9. The electronic circuit according to claim 1, wherein the measurement circuit comprises a peak detector.

10. The electronic circuit according to claim 1, wherein the adjustable output load comprises adjustable resistor.

11. The electronic circuit according to claim 1, wherein the adjustable output load comprises a switchable resistor array.

12. The electronic circuit according to claim 1, wherein the output stage comprises a transistor amplifier.

13. The electronic circuit according to claim 1, wherein the transducer is a differential transducer.

14. A microphone comprising the electronic circuit according to claim 1 and comprising a transducer.

15. The microphone of claim 14, wherein the transducer is fabricated in micro-electro-mechanical systems technology.

16. The electronic circuit according to claim 4, wherein the automatic control circuit is configured to adjust at least one impedance value of the respective adjustable circuit elements of the two-terminal mode configuration network.

Description

[0024] Further features, refinements and expediencies will become apparent from the following description of the exemplary embodiments in connection with the figures. These are as follows:

[0025] FIG. 1 a block diagram of a first exemplary embodiment of a microphone,

[0026] FIG. 2 a block diagram of a second exemplary embodiment of a microphone and

[0027] FIG. 3 a block diagram of a third exemplary embodiment of a microphone.

[0028] Elements of the same design and function that appear in different figures are identified by the same reference numerals.

[0029] FIG. 1 shows a block diagram of a first exemplary embodiment of a microphone 2. The microphone 2 comprises an electronic circuit 10.

[0030] Preferably, the electronic circuit 10 is an application-specific electronic circuit (ASIC). The electronic circuit 10 may be fabricated as a die.

[0031] The microphone 2 may comprise a transducer MEMS, in particular a micro-electro-mechanical systems transducer, for converting an acoustical input signal into an electrical signal. As an example, the transducer MEMS may comprise a semiconductor material such as silicon or gallium arsenide. The transducer MEMS may comprise a diaphragm and one or more back-plates. As an example, the distance between the diaphragm and a back-plate may be in a range of 1 m to 10 m.

[0032] In FIG. 1 the transducer MEMS is exemplarily configured as a single-ended transducer.

[0033] The microphone 2 may comprise a transducer die and the ASIC die comprising the electronic circuit 10. The shown electronic circuit 10 may also be used with other transducers than a micro-electro-mechanical systems transducer. The microphone 2 may be used in a headset, for example.

[0034] The transducer MEMS is electrically connected to the electronic circuit 10. In particular, the electronic circuit 10 may process an electrical signal of the transducer MEMS.

[0035] The electronic circuit 10 comprises an input stage Pre_amp and an output stage T_amp, an adjustable output load RS, a measurement circuit P_det, and an automatic control circuit ACC. An input of the input stage Pre_amp is coupled to a first connection of the transducer MEMS for receiving the electrical signal of the transducer MEMS.

[0036] The output stage T_amp is configured and arranged to receive an output signal of the input stage Pre_amp. The output stage T_amp may comprise a transistor 20, which may function as a transistor amplifier.

[0037] The measurement circuit P_det is configured and arranged to measure an output signal of the input stage Pre_amp. The measurement circuit P_det may comprise a peak detector.

[0038] The adjustable output load RS may be configured so that the output stage T_amp draws different levels of current depending on the sound pressure level.

[0039] The automatic control circuit ACC is arranged and configured to adjust the output load RS dependent on the output signal of the input stage Pre_amp, in particular dependent on a measurement result of the measurement circuit P_det.

[0040] The adjustable output load RS may comprise an adjustable resistor. The adjustable output load RS may comprise a switchable resistor array, and the automatic control circuit ACC may be configured to control a switch-setting of the switchable resistor array.

[0041] Furthermore, the electronic circuit 10 may provide the transducer MEMS with a bias voltage, which is not shown in detail in FIG. 1.

[0042] The electronic circuit 10 may be operable in a two-terminal mode and may comprise a first terminal MIC_VDD configured for microphone output and power supply.

[0043] A resistor RBIAS may be located in the connection between the first terminal MIC_VDD and the power supply VDD. The resistor RBIAS is connected in series to the power supply VDD.

[0044] The electronic circuit 10 comprises a second terminal MIC_GND for connecting the electronic circuit 10 to ground. The transducer MEMS may also be connected to ground.

[0045] The microphone 2 may comprise a two-terminal mode configuration network coupled to a third terminal MIC_OUT and/or coupled in parallel to the output load RS.

[0046] The two-terminal mode configuration network may comprise a first resistor RLAC and a second resistor RLDC. In the two-terminal mode two resistors RLAC, RLDC may be used in order to adjust a sensitivity of the microphone 2. The first resistor RLAC may be arranged in series to a capacitor CL. The second resistor RLDC may be arranged in parallel to the first resistor RLAC and the capacitor CL.

[0047] Preferably, the capacitor CL may not be part of the electronic circuit 10 and may be arranged eternally on a PCB. The capacitor CL may be configured as a discrete component.

[0048] The first resistor RLAC and/or second resistor RLDC may also not be part of the electronic circuit 10 and may be arranged externally on a PCB. The first resistor RLAC and second resistor RLDC may be configured as discrete components. Such an approach offers high flexibility in view of adjusting the sensitivity and provides the advantage of minor variations in sensitivity as process tolerances do not play any role in this case.

[0049] Without an applied signal and for sound pressure levels below a given threshold (for example 105 db SPL), and for given values of the output load RS (for example 30 kOhm), for the first resistor RLAC (for example 2 kOhm) and for the second resistor RLDC (for example 15 kOhm), the output stage T_amp draws a current Ivdd of 50 A and the two-wire operation mode sensitivity may be about 44 dBV. In this configuration the microphone 2 may reach the 10% THD level when the sound pressure level reaches a given limit (for example 100 dB SPL).

[0050] When a sound pressure level larger than the given threshold is detected by the measurement circuit P_det, the automatic control circuit ACC reduces the value of the output load RS and, as a result, the current Ivdd running into the output stage T_amp is increased.

[0051] Changing the DC current in the output stage T_amp may cause glitches during the current switching. Preferably the electronic circuit 10 comprises a circuit (glitch eater circuit) to suppress the glitches on the microphone output.

[0052] FIG. 2 shows a block diagram of a second exemplary embodiment of the microphone 2.

[0053] In this case the transducer MEMS is configured as a differential transducer and the input stage Pre_amp is configured as a differential-to-single-ended input stage Pre_amp. With such a configuration higher sound pressure levels may be reached as other sources of non-linearity, for example a non-linearity of the transducer MEMS and/or the input stage Pre_amp, may be compensated.

[0054] FIG. 3 shows a block diagram of a third exemplary embodiment of the microphone 2.

[0055] In comparison to FIG. 1 or 2, the first resistor RLAC and the second resistor RLDC are part of the electronic circuit 10 and may be arranged on the same die as the electronic circuit 10.

[0056] Preferably, the first resistor RLAC and/or second resistor RLDC and/or a gain of the input stage Pre_amp are adjustable and the automatic control circuit ACC is configured to adjust the gain of the input stage Pre_amp and/or at least one impedance value of the respective adjustable circuit elements of the two-terminal mode configuration network.

[0057] In the case the current Ivdd is changed, the resulting change in sensitivity may be compensated by reconfiguring the first resistor RLAC and/or second resistor RLDC and/or input stage Pre_amp, and the sensitivity may be kept constant.

[0058] Thereby, the spread of the sensitivity in the two-wire mode may be reduced. This spread may arise not only from the resistors but also from the overall spread of the microphone sensitivity. Thus, the total spread can be reduced. In particular, a sensitivity adjustment can be achieved by tuning the first resistor RLAC and second resistor RLDC. Furthermore, also the current consumption and the THD performance of the microphone 2 may be adjusted, in particular by tuning the output load RS and the gain of the input stage Pre_amp.

REFERENCE NUMERALS

[0059] 2 microphone
10 electronic circuit
ACC automatic control circuit
CL capacitor
Ivdd current of the output stage
MEMS transducer
MIC_GND second terminal
MIC_OUT third terminal
MIC_VDD first terminal
P_det measurement circuit
Pre_amp input stage
RBIAS resistor
RLAC first resistor
RLDC second resistor
RS output load
T_amp output stage
VDD power supply