Microphone biasing circuitry and method thereof
A host device for use with a removable peripheral apparatus having a microphone, and to the biasing circuitry for said microphone. The host device may have a device connector for forming a mating connection with a respective peripheral connector. A source of bias is arranged to supply an electrical bias to a device microphone contact of the device connector via a biasing path. A capacitor is connected between a reference voltage node and a capacitor node of the biasing path. A first switch is located between the capacitor node and the device microphone contact. Detection circuitry detects disconnection of the peripheral connector and device connector; and control circuitry controls the switch to disable the biasing path.
1. A host device for use with a removable peripheral apparatus having a microphone, the host device comprising:
a device connector capable of forming a mating connection with a respective peripheral connector of the removable peripheral device, the device connector having a device microphone contact and a device ground contact;
biasing circuitry for supplying an electrical bias to said device microphone contact via a biasing path;
a first switch operable to electrically connect said device microphone contact to said device ground contact;
detection circuitry for detecting disconnection of the peripheral connector and device connector; and
a controller for controlling said first switch to connect the microphone contact to the device ground contact in response to detection of disconnection of the peripheral connector and device connector.
2. A host device as claimed in claim 1 , further comprising a second switch located in the biasing path and operable to disable the biasing path wherein the controller is configured to control the second switch to disable the biasing path in response to said in response to detection of disconnection of the peripheral connector and device connector.
3. A host device as claimed in claim 1 further comprising a separate ground return path between the device ground contact and a ground reference node.
4. A host device as claimed in claim 1 wherein said biasing circuitry and said first switch are formed as part of a first integrated circuit, wherein the first integrated circuit comprises:
a microphone terminal connected, in use, to said device microphone contact;
a first ground terminal coupled to a ground reference node to provide an on-chip ground; and
a second ground terminal coupled, in use, to said device ground contact;
wherein said first switch is operable to connect said microphone terminal to said second ground terminal.
5. A host device as claimed in claim 4 wherein the biasing circuitry is configured to generate said electrical bias with respect to a voltage at the second ground terminal.
6. A host device as claimed in claim 5 wherein the biasing circuitry is coupled to said first ground terminal and to said second ground terminal.
7. A host device as claimed in claim 6 , wherein the biasing circuitry comprises a first circuit branch for generating a first current based on a reference voltage defined with respect to a voltage at the first ground node and a second circuit branch for supplying a second current based on the first current to a resistor coupled to the second ground node.
8. A host device as claimed in claim 4 , further comprising input circuitry for receiving a microphone signal from said microphone contact wherein the input circuitry is coupled to said microphone terminal and said second ground terminal.
9. A host device as claimed in claim 8 , wherein the input circuitry comprises a differential or pseudo-differential amplifier coupled to said microphone terminal and said second ground terminal.
10. A host device as claimed in claim 8 , wherein a DC blocking capacitor is situated between the device microphone contact and said input circuitry.
11. A host device as claimed in claim 10 , further comprising an input switch located between the DC blocking capacitor and the input circuitry, which operates in response to said detection of disconnection.
12. A host device as claimed in claim 4 , wherein the first integrated circuit further comprises impedance measurement circuitry configured to measure a microphone impedance wherein the impedance measurement circuitry is coupled to said microphone terminal and said second ground terminal.
13. A host device as claimed in claim 4 , wherein the signal path between the device ground contact and the second ground terminal does not have a DC blocking capacitor.
14. A host device as claimed in claim 4 , wherein the first integrated circuit further comprises a speaker drive amplifier, wherein the speaker drive amplifier is coupled to said first ground terminal and to said second ground terminal.
15. A host device as claimed in any claim 1 , wherein the device connector is a socket for receiving a jack plug peripheral connector.
16. A host device for use with a removable peripheral apparatus having a microphone, the host device comprising:
a device connector capable of forming a mating connection with a respective peripheral connector of the removable peripheral device, the device connector having a device microphone contact and a device ground contact; and
a first integrated circuit comprising biasing circuitry generating an electrical bias for device microphone contact, the first integrated circuit comprising:
a bias terminal for outputting the electrical bias to the device microphone contact;
a first ground terminal coupled to a ground reference node to provide an on-chip ground; and
a second ground terminal coupled, in use, to said device ground contact;
wherein the biasing circuitry is configured to generate said electrical bias with respect to a voltage at the second ground terminal.
17. A host device as claimed in claim 16 , further comprising:
a biasing path between the biasing circuitry and the device microphone contact;
a biasing path switch operable to disable said bias path;
detection circuitry for detecting disconnection of the peripheral connector and device connector; and
a controller for controlling said biasing path switch to disable the biasing path in response to detection of disconnection of the peripheral connector and device connector.
18. A host device as claimed in claim 16 , further comprising further comprising
a microphone terminal connected, in use, to said device microphone contact to receive a microphone signal;
a first switch operable to connect said microphone terminal to said second ground terminal;
detection circuitry for detecting disconnection of the peripheral connector and device connector; and
a controller for controlling said first switch to connect the microphone terminal to the second ground terminal in response to detection of disconnection of the peripheral connector and device connector.
19. An integrated circuit for interfacing with a device connector for connecting to a removable peripheral audio apparatus having a microphone, the integrated circuit comprising:
biasing circuitry configured to generate an electrical bias at a biasing terminal for biasing said microphone;
a first ground terminal configured to be coupled, in use, to a ground reference node to provide an on-chip ground;
input circuitry for receiving an input microphone signal from a microphone terminal;
a second ground terminal for receiving a voltage from a ground contact of the device connector.
20. An integrated circuit as claimed in claim 19 , further comprising a switch operable to disconnect the biasing circuitry from the biasing terminal.