INCREASING GROUND NOISE REJECTION IN AUDIO SYSTEMS

• US 20140093103A1
• Filed: 09/28/2012
• Published: 04/03/2014
• Est. Priority Date: 09/28/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Breece, David C. III, Johanningsmeier, Nathan, Yang, Cara S.
• Granted Patent: US 9,099,967 B2
• Time in Patent Office: Days
• US Class Current: 381/120
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 2203/45528 the FBC comprising one or more passive resistors and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45594 the IC comprising one or more resistors, which are not biasing resistor
• CPC Class Codes: H03F 3/181 Low-frequency amplifiers, e.g. audio preamplifiers
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602
• CPC Class Codes: H04R 2420/05 Detection of connection of loudspeakers or headphones to amplifiers
• CPC Class Codes: H04R 5/04 Circuit arrangements, e.g. for selective connection of amplifier inputs/outputs to loudspeakers, for loudspeaker detection, or for adaptation of settings to personal preferences or hearing impairments combinations of amplifiers H03F3/68; stereophonic systems H04S

Abstract

An audio source device has an audio connector to which an external load can be connected. An audio signal is amplified and then driven through the connector, wherein the amplification process uses feedback from the return pin of the connector. The return pin is directly connected to a ground break resistor circuit. The ground break resistor circuit is connected between the return pin of the audio connector and circuit ground. A determination is made as to whether the connected external load has a low impedance or a high impedance. When a low impedance load is detected, such as a headset, the ground break resistor circuit is essentially short-circuited. When a high impedance load is detected, the ground break resistor circuit is maintained and its value is set in accordance with the detected load. Other embodiments are also described.

Claims

1. An audio apparatus comprising:

an audio source;

an audio connector having a signal out pin and a return pin to be connected to an external audio load;

a differential input amplifier having a signal input coupled to the audio source, an output coupled to the signal out pin of the connector, and a feedback input;

a variable resistor circuit to provide variable resistance between a first node and a second node, the variable resistor circuit having a control input for setting the variable resistance, wherein the first node is directly connected to the return pin of the connector and to the feedback input of the differential input amplifier, and the second node is directly connected to a ground plane of the apparatus;

a switch circuit having a first terminal coupled to the first node, a second terminal coupled to the second node, and a control input for setting the switch circuit into an open state and a closed state; and

a load detector having outputs that are coupled to the control inputs of the variable resistor circuit and the switch circuit, wherein the load detector is used to detect the type of external audio load that is connected to the connector and on that basis a) set the switch circuit into one of the open state and the closed state, and b) set the variable resistance.

2. The audio apparatus of claim 1 wherein the audio source comprises:

a digital audio processor; and

a digital to analog converter having an input coupled to the digital audio processor and an output coupled to the signal input of the differential input amplifier.

3. The audio apparatus of claim 1 further comprising a portable personal audio device housing in which the audio source and the connector are integrated.

4. The audio apparatus of claim 3 further comprising:

a further connector having a signal pin and a return pin to be connected to the external audio load; and

a data driver circuit having an output coupled to the signal pin of the further connector, and being coupled to the ground plane of the apparatus and to the return pin of the further connector.

5. The audio apparatus of claim 1 further comprising:

an AC-DC power converter; and

an AC wall-power connector coupled to an input of the AC-DC power converter, the wall power connector having a power pin, a neutral pin, and a ground pin, wherein the ground pin of the power connector is coupled to the ground plane of the audio apparatus.

6. The audio apparatus of claim 1 further comprising:

a signal-in amplifier having an input,

wherein the audio connector has a further signal out pin and a signal-in pin, the signal-in pin being coupled to the input of the signal-in amplifier.

7. An audio apparatus comprising:

means for producing an audio signal;

means for amplifying the audio signal while coupled to a ground plane of the apparatus;

means for electrically connecting the amplified audio signal to an external sound producing device through a signal out pin and a return pin;

means for providing a variable resistance between a first node and a second node, wherein the first node is directly connected to the return pin and to a feedback input of the amplifier means, and the second node is directly connected to the ground plane of the apparatus;

means for alternately creating essentially a short circuit and essentially an open circuit, connected to the first and second nodes; and

means for sensing impedance out through the signal out pin, and on that basis a) controlling whether the first and second nodes are connected by essentially the short circuit or by the open circuit, and b) setting the variable resistance.

8. The apparatus of claim 7 further comprising means for housing a) the audio signal producer means, b) the amplifier means, and c) the electrical connector means.

9. The apparatus of claim 7 further comprising:

means for driving a data signal while being coupled to the ground plane of the apparatus; and

a further means for electrically connecting the driven data signal to the external sound producing device.

10. The apparatus of claim 7 further comprising:

means for converting AC power to DC power; and

a further means for electrically connecting the power converting means to an AC wall outlet, including a ground pin that is coupled to the ground plane of the audio apparatus.

11. The audio apparatus of claim 7 wherein the electrical connector means has a further signal out pin and a signal-in pin, the audio apparatus further comprising means for amplifying an input signal received through the signal-in pin.

12. A method for operating an audio source device having an audio connector, comprising:

determining that one of a low impedance load and a high impedance load is connected to a signal-out pin of the audio connector, and, based on the determined load, one of

a) essentially short circuiting a variable resistor that is connected in series between a return pin of the audio connector and a circuit ground,

b) setting a resistance value of the variable resistor in accordance with the determined load, and maintaining the as-set variable resistor as connected in series between the return pin and the circuit ground; and

amplifying an audio signal that is then driven through the signal-out pin of the connector, while using a) feedback from the return pin of the connector and b) a power supply return path through the circuit ground.

13. The method of claim 12 wherein determining the load comprises sensing impedance through the signal-out pin of the audio connector and comparing the sensed impedance to a predetermined range.

14. The method of claim 12 further comprising:

driving a data signal, while using the circuit ground, through a data connector, wherein a return pin of the data connector and the return pin of the audio connector are connected to each other by an external low impedance path.

15. The method of claim 12 further comprising:

converting AC power from an AC wall outlet into DC power, to enable amplifying the audio signal, while a ground pin of the AC wall outlet is connected to the circuit ground through a low impedance path.

16. The method of claim 12 further comprising:

amplifying a further audio signal that is then driven through a further signal-out pin of the audio connector, while using a) feedback from the return pin of the connector and b) a power supply return path through the circuit ground.

17. The method of claim 16 further comprising amplifying an input signal received through a signal-in pin of the audio connector.