Appeal No. 2000-1939
Application 08/791,281
transistors M3 and M4. Switches SW1 and SW2 presumably are
constructed in the same way.
This prior art switching circuitry suffers from harmonic
distortion caused by current injection occurring during the
turning off of transistor M4, as explained infra. This is not a
problem during the turning off of transistors M1-M3 for the
following reasons. When transistor M1 is turned off, transistor
M4 is already off, with the result that no current can be
injected from transistor M1 into the floating capacitor.
Specification at 3, lines 29-34. Likewise, when transistor M2 is
turned off, transistor M3 is already off. Id. Although
transistor M3 is turned off while transistor M2 is still on,
thereby causing charge to be injected from transistor M3 into
capacitor C3, the amount of injected current is fixed and thus
causes some voltage offset but no harmonic distortion. Id. at 4,
lines 4-5 and 12-15. The reason is that "the voltage across M3
-3-
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