Method and apparatus for controlling impedance
DCFirst Claim
Patent Images
1. An integrated circuit having a variable impedance component comprising:
- an output terminal;
a voltage potential terminal;
a variable impedance circuit connected to said voltage potential terminal and said output terminal, the impedance value of said variable impedance circuit being variable in accordance with an applied control signal; and
a passive impedance connected in series with said variable impedance circuit and between said voltage potential terminal and said output terminal.
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Abstract
A passive resistive element is provided in series with a digital variable impedance to produce a highly linear output impedance for a transmission path over a wide range of operating conditions.
29 Citations
37 Claims
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1. An integrated circuit having a variable impedance component comprising:
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an output terminal; a voltage potential terminal; a variable impedance circuit connected to said voltage potential terminal and said output terminal, the impedance value of said variable impedance circuit being variable in accordance with an applied control signal; and a passive impedance connected in series with said variable impedance circuit and between said voltage potential terminal and said output terminal. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An integrated circuit having a variable impedance component comprising:
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an output terminal; a first voltage potential terminal; a second voltage potential terminal; a first impedance control circuit connected to said output terminal, said first impedance control circuit selectively connecting said output terminal to said first voltage potential terminal through a first variable impedance in response to a first applied logic signal, the impedance of said first variable impedance being variable in accordance with a first applied control signal; a second impedance control circuit connected to said output terminal, said second impedance control circuit selectively connecting said output terminal to said second voltage potential terminal through a second variable impedance in response to a second applied logic signal, the impedance of said second variable impedance being variable in accordance with a second applied control signal; and at least one passive resistive element which is connected in series with at least one of said first and second variable impedances when said first and second variable impedances are selectively connected to said output terminal and a respective voltage potential terminal. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. An impedance matching output buffer comprising:
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an input terminal; an output terminal; a first voltage potential terminal; a second voltage potential terminal; a first impedance control circuit connected to said input terminal and said output terminal, said first impedance control circuit selectively connecting said output terminal to said first voltage potential terminal through a first variable impedance in response to a first applied logic signal at said input terminal, the impedance of said first variable impedance being variable in accordance with a first applied control signal; a second impedance control circuit connected to said input terminal and said output terminal, said second impedance control circuit selectively connecting said output terminal to said second voltage potential terminal through a second variable impedance in response to said second applied logic signal at said input terminal, the impedance of said second variable impedance being variable in accordance with a second applied control signal; and at least one passive resistive element which is connected in series with at least one of said first and second variable impedances when said first and second variable impedances are selectively connected to said output terminal and a respective voltage potential terminal. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25)
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26. A method providing output impedance for a communication path comprising the steps of:
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switching a variable impedance element in series between an output terminal connected to said communications path and a voltage potential terminal, in response to an applied logic signal; adjusting the impedance of said variable impedance element in accordance with an applied control signal; and connecting a passive resistive element in series with said variable impedance element and between said voltage potential terminal and said output terminal at least when said variable impedance element is switched in series between said output terminal and said voltage potential terminal. - View Dependent Claims (27, 28, 29, 30)
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31. A method of providing an output impedance for a communications path comprising the steps of:
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switching a first variable impedance in series between an output terminal connectable to said communication path and a first voltage potential terminal in response to a first applied logic signal; adjusting the impedance with said first variable impedance in accordance with a first applied control signal; switching a second variable impedance in series between said output terminal and a second voltage potential terminal in response to a second applied logic signal; adjusting the impedance of said second variable impedance in accordance with a second applied control signal; connecting at least one passive resistive element in series with said first and second variable impedances at least when said first and second variable impedance are switched in series between said output terminal and a respective voltage potential terminal. - View Dependent Claims (32, 33, 34, 35, 36, 37)
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Specification