Interface circuit for connecting a microphone circuit to a preamplifier

A microphone preamplifier circuit comprising a preamplifier, an interface circuit and a microphone circuit;

• the microphone circuit comprises a microphone and at least an output node and the preamplifier comprises at least an input node adapted to be connected to the output node through the interface circuit, the interface circuit comprises:
• at least a decoupling capacitor for DC decoupling the input node from the output node, the decoupling capacitor having a first end connected, or configured to be connected, to the input node and a second end connected or configured to be connected to the output node;
• at least one active circuit comprising:
• a resistor with a first end connected to the first end of the decoupling capacitor;
• a first MOS device and a second MOS device, each of the MOS devices having a respective gate terminal, a drain terminal and a source terminal, the gate terminal of the second MOS device being connected to the source terminal of the first MOS device, and wherein the first end of the resistor is connected to the gate terminal of the first MOS device and the second end of the resistor is connected to the drain terminal of the first MOS device and to the source terminal of the second MOS device;
• and
• a biasing circuit connected to a second end of the resistor for biasing the input node of the preamplifier with a desired bias voltage;
• the interface circuit being configured to operatively act as a resistance multiplier and to have an equivalent resistance depending on a resistance of the resistor that together with the decoupling capacitor defines a high-pass filter operatively connected or configured to be connected between the microphone and the preamplifier.

A device provided with audio recording capabilities, the device comprising a microphone system comprising at least one microphone circuit and a microphone preamplifier circuit;

• the microphone circuit comprises a microphone and at least an output node;
• the microphone preamplifier circuit comprises a preamplifier and an interface circuit;
• the preamplifier comprises at least an input node adapted to be connected to the output node through the interface circuit, the interface circuit comprising:
• at least a decoupling capacitor for DC decoupling the input node from the output node, the decoupling capacitor having a first end connected, or configured to be connected, to the input node and a second end connected or configured to be connected to the output node;
• at least one active circuit comprising:
• a resistor with a first end connected to the first end of the decoupling capacitor;
• a first MOS device and a second MOS device, each of the MOS devices having a respective gate terminal, a drain terminal and a source terminal, the gate terminal of the second MOS device being connected to the source terminal of the first MOS device, and wherein the first end of the resistor is connected to the gate terminal of the first MOS device and the second end of the resistor is connected to the drain terminal of the first MOS device and to the source terminal of the second MOS device;
• and
• a biasing circuit connected to a second end of the resistor for biasing the input node of the preamplifier with a desired bias voltage;
• the interface circuit being configured to operatively act as a resistance multiplier and to have an equivalent resistance depending on a resistance of the resistor that together with the decoupling capacitor defines a high-pass filter operatively connected or configured to be connected between the microphone and the preamplifier.