Fast Precision Charge Pump for Condenser Microphones
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Solution Overview
Problem
Prior art charge pumps used for biasing condenser microphones exhibit large ramp-up times due to high source impedance and large capacitive loads, which hinder efficient DC voltage generation.
Innovation Solution
A charge pump system comprising a capacitive electro-acoustic transducer element, a charge pump, and a controllable or programmable current source that maintains low output impedance by drawing a predetermined DC current, with a voltage divider and error amplifier to regulate the DC bias voltage and minimize noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a charge pump is used to generate DC bias voltage for condenser microphones, then DC voltage generation is achieved, but the ramp-up time is large due to high source impedance and large capacitive loads
Solution Approach 1:
The charge pump circuit is divided into multiple pumping stages with inter-stage coupling capacitors. This segmentation allows the large capacitive load to be charged in stages rather than all at once, reducing the ramp-up time while managing the source impedance through distributed capacitance values.
Solution Approach 2:
Inter-stage coupling capacitors are pre-charged to intermediate voltage levels during the pumping process. This preliminary action allows the final output capacitor to be charged more quickly from a higher starting voltage, thereby reducing the overall ramp-up time of the DC bias voltage.
2Loss of time
If a charge pump with high source impedance is used, then DC bias voltage generation is simplified, but the ramp-up time increases due to large capacitive loads
Solution Approach 1:
The output impedance of the charge pump is dynamically managed by using multiple pumping stages with optimized capacitance values. The inter-stage coupling capacitors are sized to provide sufficient charge transfer while maintaining a low effective output impedance, thus reducing ramp-up time without overly complicating the circuit operation.
3Measurement precision
If the charge pump output is directly connected to the capacitive load, then the circuit is simple, but the DC output voltage cannot be accurately set to a desired voltage
Solution Approach 1:
A feedback network consisting of resistors is connected to the output of the charge pump. This feedback network provides voltage division and feedback signals that enable accurate setting of the DC output voltage to a desired level. The feedback mechanism allows precise voltage control while maintaining a relatively simple overall circuit structure.
Data Source
AI summary
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.