Increasing ground noise rejection in audio systems
First Claim
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 a variable resistance that is within a range of 1 to 60 Ohms 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 connecter 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.
1 Assignment
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Accused Products
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.
19 Citations
17 Claims
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1. An audio apparatus comprising:
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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 a variable resistance that is within a range of 1 to 60 Ohms 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 connecter 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. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An audio apparatus comprising:
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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 path that connects a first node and a second node, wherein the first node is directly connected to the return pin and is directly connected, but not through the variable resistance path, 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 a short circuit and an open circuit, across the first and second nodes; and means for sensing impedance out through the signal out pin, and on that basis a) controlling whether or not the first and second nodes are short circuited to each other by said creating means, and b) setting resistance of the variable resistance path. - View Dependent Claims (8, 9, 10, 11)
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12. A method for operating an audio source device having an audio connector, comprising:
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determining that one of a low impedance load or a high impedance load is connected to a signal-out pin of the audio connector, and, based on the determined load, one of a) short circuiting across a variable resistor that provides a variable resistance within a range of 1 to 60 Ohms connected in series between a return pin of the audio connector and a circuit ground, or 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. - View Dependent Claims (13, 14, 15, 16, 17)
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Specification