Fast precision charge pump
The present invention relates to a condenser microphone assembly comprising a capacitive electro-acoustic transducer element comprising a diaphragm and a back-plate operatively connected to a DC bias voltage, a fast charge pump adapted to generate the DC bias voltage, and a controllable or programmable current source operatively connected to the DC bias voltage to draw a predetermined DC current there from. The controllable or programmable current source is responsive to a difference between a representative of a detected DC bias voltage and a DC reference voltage.
1. A condenser microphone assembly, comprising:
a capacitive electro-acoustic transducer element comprising a diaphragm and a back-plate operatively connected to a DC bias voltage;
a charge pump adapted to generate the DC bias voltage; and
a controllable or programmable current source operatively connected to the DC bias voltage to draw a predetermined DC current there from when an output voltage of the charge pump exceeds a predefined value so as to maintain a low output impedance of the charge pump under start-up and steady-state loading,
wherein the controllable or programmable current source is responsive to a difference between a representative of a detected DC bias voltage and a DC reference voltage to maintain a substantially constant DC bias voltage under steady-state loading.
2. A condenser microphone assembly according to claim 1 , further comprising a voltage divider operatively connected to the DC bias voltage of the charge pump, said voltage divider being adapted to provide the representative of the detected DC bias voltage.
3. A condenser microphone assembly according to claim 2 , further comprising an error amplifier for comparing the representative of the detected DC bias voltage and the DC reference voltage, the error amplifier being adapted to generate a control signal in response to said comparison and apply said control signal to control the controllable or programmable current source.
4. A condenser microphone assembly according to claim 3 , further comprising a voltage generator circuit adapted to generate the DC reference voltage.
5. A condenser microphone assembly according to claim 1 , wherein the DC bias voltage is provided to the electro-acoustic transducer element via a high impedance circuit.
6. A condenser microphone assembly according to claim 5 , wherein the high impedance circuit comprises a pair of cross-coupled diodes.
7. A condenser microphone assembly according to claim 1 , further comprising a noise filtration capacitor operatively connected to the DC bias voltage.
8. A condenser microphone assembly according to claim 1 , further comprising signal processing circuitry operationally connected to the electro-acoustic transducer element so as to process signals generated by said transducer element.
9. A condenser microphone assembly according to claim 8 , wherein the signal processing circuitry comprises a buffer or a preamplifier operationally connected to the electro-acoustic transducer.
10. A condenser microphone assembly according to claim 9 , wherein the signal processing circuitry further comprises an A/D converter operationally connected to the buffer or preamplifier.
11. A DC voltage supply circuitry for generating a DC bias voltage for being applied as a DC voltage difference between a diaphragm and a back-plate of an associated capacitive electro-acoustic transducer element, the DC voltage supply circuitry comprising:
a semiconductor die comprising a charge pump for generating and providing the DC bias voltage for the capacitive electro-acoustic transducer element when an output voltage of the charge pump exceeds a predefined value so as to maintain a low output impedance of the charge pump under start-up and steady-state loading; and
a controllable or programmable current source operatively connected to the DC bias voltage, wherein the current source is controllable in response to a comparison between a representative of a detected DC bias voltage and a DC reference voltage to maintain a substantially constant DC bias voltage under steady-state loading.
12. A DC supply circuitry according to claim 11 , further comprising a voltage divider operatively connected to the DC bias voltage, said voltage divider being adapted to provide the representative of the detected DC bias voltage.
13. A DC supply circuitry according to claim 11 , further comprising an error amplifier for comparing the representative of the detected DC bias voltage and the reference DC voltage, the error amplifier being adapted to generate a control signal in response to said comparison and apply said control signal to control the controllable or programmable current source.
14. A DC supply circuitry according to claim 11 , further comprising a noise filtration capacitor operatively connected to the DC bias voltage.
15. A DC supply circuitry according to claim 11 , further comprising a voltage generator adapted to generate the reference DC voltage.
16. A method for generating a DC bias voltage to be applied as a DC voltage difference between a diaphragm and a back-plate of a capacitive electro-acoustic transducer element, the method comprising:
applying a clock signal to a charge pump for generating and providing the DC bias voltage when an output voltage of the charge pump exceeds a predefined value so as to maintain a low output impedance of the charge pump under start-up and steady-state loading;
providing the DC bias voltage to a controllable or programmable current source of the capacitive electro-acoustic transducer element;
comparing a representative of a detected DC bias voltage and a reference DC voltage;
generating, in response to said comparison, a control signal; and
controlling the current source in response to the control signal to maintain a substantially constant DC bias voltage under steady-state loading.
17. A method according to claim 16 , wherein a current load of the current source falls within a first current range if the representative of the measured DC bias voltage is smaller than the reference DC voltage.
18. A method according to claim 16 , wherein a current load of the current source falls within a second current range if the representative of the measured DC bias voltage is higher than the reference DC voltage.
19. A method according to claim 18 , wherein current loads of the second current range are higher than current loads of the first current range.
20. A condenser microphone assembly, comprising,
a capacitive electro-acoustic transducer element comprising a diaphragm and a back-plate;
a semiconductor die comprising a voltage multiplier for generating and providing a DC bias voltage via an output terminal when an output voltage of the voltage multiplier exceeds a predetermined value so as to maintain a low output impedance of the voltage multiplier under start-up and steady-state loading, said DC bias voltage being applied as a DC voltage difference between the diaphragm and the back-plate; and
a controllable or programmable current source operatively connected to the output terminal of the voltage multiplier, the controllable or programmable current source being controllable in response to a comparison between a representative of a detected DC bias voltage level and a reference voltage level to maintain a substantially constant DC bias voltage under steady-state loading.