Audio jack detection circuit
This document discusses, among other things, a detection system configured to identify a type of a pole of a four-pole audio jack using first and second comparators. The detection system can include a bias circuit configured to bias a detection input coupled to the pole, and first and second comparators configured to compare the detection input to respective first and second thresholds to provide an indication of the type of the pole.
1. A detection system, comprising:
a bias circuit configured to bias a detection input selectively coupled to a pole of a four-pole audio jack; and
first and second comparators configured to compare a value of the detection input to respective first and second thresholds and to provide an indication of a type of the pole,
wherein the bias circuit includes:
a bias resistor configured to receive a supply voltage;
a current source; and
a bias switch configure to selectively couple the current source to the detection input, wherein the current source and the bias switch are in parallel with the bias resistor.
2. The system of claim 1 , wherein the four-pole audio jack includes:
a ground (GND) pole; and
a microphone (MIC) pole; and
wherein the type of the pole includes a MIC pole or a GND pole.
3. The system of claim 1 , wherein the type of the pole includes a MIC pole, a GND pole, or a floating pole.
4. The system of claim 1 , wherein the first and second comparators are configured to provide an indication of an impedance at the pole.
5. The detection system of claim 1 , including:
a switch configured to automatically couple the pole to a MIC connection of a processor or to automatically couple the pole to a GND connection using information from the first and second comparators.
6. The detection system of claim 5 , wherein the first threshold is higher than the second threshold and the second threshold is higher than GND; and
wherein the switch is configured to couple the pole to the MIC connection of the processor when the value of the detection input is between the first and second thresholds.
7. The detection system of claim 5 , wherein the first threshold is higher than the second threshold and the second threshold is higher than GND; and
wherein the switch is configured to couple the pole to the GND connection of the processor when the value of the detection input is above the first and second thresholds.
8. The detection system of claim 5 , wherein the first threshold is higher than the second threshold and the second threshold is higher than GND; and
wherein the switch is configured to couple the pole to the GND connection of the processor when the value of the detection input is below the first and second thresholds.
9. The detection system of claim 1 , wherein the bias circuit includes:
a bias resistor configured to receive a supply voltage.
10. A detection method, comprising:
selectively coupling a pole of a four-pole audio jack to a detection input of a detection circuit;
biasing the detection input using a bias circuit;
comparing a value of the detection input to first and second thresholds using respective first and second comparators; and
identifying a type of the pole using the comparisons of the value of the detection input to the first and second thresholds,
wherein the bias circuit includes:
a bias resistor configured to receive a supply voltage;
a current source; and
a bias switch configured to selectively couple the current source to the detection input, wherein the current source and the bias switch are in parallel with the bias resistor.
11. The detection method of claim 10 , wherein the four-pole audio jack includes:
a ground (GND) pole; and
a microphone (MIC) pole; and
wherein the identifying the type of the pole includes identifying the pole as a MIC pole or a GND pole.
12. The detection method of claim 10 , wherein the selectively coupling the pole includes:
first, selectively coupling a first pole of the four-pole audio jack to the detection input to identify the first pole as the MIC pole or the GND pole; and
second, separately selectively coupling a second pole of the four-pole audio jack to the detection circuit to identify the second pole as the MIC pole or the GND pole.
13. The detection method of claim 10 , wherein the biasing the detection input includes:
biasing the detection input using a voltage source to determine no connection at the first pole; and
biasing the detection input using a current source to determine connection at the first pole.
14. The detection method of claim 10 , wherein the first threshold is higher than the second threshold and the second threshold is higher than GND; and
wherein the identifying the pole includes identifying the pole as the MIC pole when the value of the detection input is between the first and second thresholds.
15. The detection method of claim 10 , wherein the first threshold is higher than the second threshold and the second threshold is higher than GND; and
wherein the identifying the pole includes identifying the pole as the GND pole when the value of the detection input is above or below the first and second thresholds.
16. The detection method of claim 10 , including:
automatically coupling the identified pole to a MIC connection of a processor or to a GND connection of a processor using a switch.
17. The detection method of claim 10 , wherein the identifying the type of the pole includes identifying the pole as a MIC pole, a GND pole, or a floating pole.
18. A detection system, comprising:
a bias circuit configured to bias a detection input selectively coupled to a pole of a four-pole audio jack, the four-pole audio jack including:
a ground (GND) pole; and
a microphone (MIC) pole;
first and second comparators configured to compare a value of the detection input to respective first and second thresholds and to provide an indication of the pole as a MIC pole or a GND pole; and
a switch configured to automatically couple the pole to a MIC connection of a processor or to automatically couple the pole to a GND connection using information from the first and second comparators,
wherein the bias circuit includes:
a bias resistor configured to receive a supply voltage;
a current source; and
a bias switch configure to selectively couple the current source to the detection input, wherein the current source and the bias switch are in parallel with the bias resistor.
19. The detection system of claim 18 , wherein the first threshold is higher than the second threshold and the second threshold is higher than GND; and
wherein the switch is configured to couple the pole to the MIC connection of the processor when the value of the detection input is between the first and second thresholds.
20. The detection system of claim 18 , wherein the first threshold is higher than the second threshold and the second threshold is higher than GND; and
wherein the switch is configured to couple the pole to the GND connection of the processor when the value of the detection input is above or below the first and second thresholds.