Appeal 2007-1540
Application 10/280,788
the input of an amplifier. Col. 2, ll. 44-47. The gate of the native transistor
M3 is supplied with a regulated signal, Lv13COMP13EN, such that the
voltage output of the transistor will not be higher then the regulated supply
VCC. Col. 2, ll. 58-62. The native transistor has a very low threshold
voltage, which eliminates the dead zone and allows for input protection
because of the regulated signal applied to the gate. Col. 3, ll. 18-29. A
clamp circuit, item 104, is connected between the output of the native
transistor and the input of the amplifier. Col. 2, ll. 44-47. The clamp circuit
contains two transistors M1 and M2, transistor M1 is configured to act as a
diode. Col. 2, ll. 66-67 and Col. 3, ll. 44-50. Cress describes the input
signal to transistor M2 as an enable to control the clamp, i.e. M2 functions as
a switch to either electrically connect or disconnect transistor M1 to the
circuit. Col. 3, ll. 29-32.
One skilled in the art would recognize that the functional equivalent
of a closed switch is hard wiring the circuit, i.e. placing a direct connection
in place of the switch. On the issue of obviousness the Supreme Court has
recently stated that “when a patent claims a structure already known in the
prior art that is altered by the mere substitution of one element for another
known in the field, the combination must do more then yield a predictable
result.” KSR Int’l Co. v. Teleflex Inc., 127 S. Ct. 1727, 1740, 82 USPQ2d
1385, 1395 (2007). In this case, we find that the substitution of a direct
connection for the switch of transistor M2 to be a substitution of known
elements, which will provide the predictable result of keeping the diode
transistor M3 enabled, i.e. keeping the circuit in one of its known states. As
such, we conclude the arrangement of Cress’s circuit with the diode
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