Claims
- 1. A signal generating apparatus comprising means for inputting a plurality of variable input signals to produce a cumulative output signal and means for selectively varying the number of said inputs, impedance-changing means in the lines of the respective input signals for providing a substantially constant impedance for the cumulative output signal independent of the number of said inputs.
- 2. Apparatus according to claim 1 wherein said impedence changing means comprises a plurality of resistance branches, each resistance In each branch being in series with a respective input signal and all the resistances being connected to a common output for the cumulative signal, means for opening the circuit between the inputs and said common output for the resistances to which no inputs are to be applied, and means varying the resistances In those lines to which the inputs are to be applied in dependence on the number of said inputs.
- 3. Apparatus according to claim 2 wherein the resistance in the path of each input signal line comprises a series of similar value resistors the total number of which in each line corresponds to a maximum number of said input signals.
- 4. A signal generating apparatus comprising means for summing a plurality of input signals to produce a cumulative output signal and means for selectively varying the number of said inputs, variable impedance means in the lines of the respective input signals for providing a substantially constant impedance for the cumulative output signal independent of the number of said inputs, said variable impedance means comprising a plurality of resistance branches each having plurality of resistances, each resistance in each branch being in series with a respective input signal and all the resistances being connected to a common output for the cumulative signal, means for opening the circuit between the inputs and said common output for the resistances to which no inputs are to be applied, and means varying the resistances in those lines to which the inputs are to be applied In dependence upon the number of said inputs, the resistances in the path of each input signal comprising a series of similar value resistors, the total number of resistors In each line corresponding to a maximum number of input signals.
Priority Claims (1)
Number |
Date |
Country |
Kind |
9208749.3 |
Apr 1992 |
GBX |
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Parent Case Info
This application is a divisional of U.S. Ser. No. 08/318,836 filed on Oct. 18, 1994, now U.S. Pat. No. 5,565,687 which is a division of PCT/GB92/01601 Sep. 2, 1992.
US Referenced Citations (5)
Divisions (1)
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Number |
Date |
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318836 |
Oct 1994 |
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