Appeal No. 95-3917
Application 07/861,144
35 U.S.C. § 103
Hochschild and Merrick
Figure 1 of Hochschild shows an operational amplifier 10 having a feedback resistor network
comprising four series-connected resistors 40, 42, 44, and 48 in parallel with series-connected resistors
36, 38 in parallel with resistor 34. The transistors 28, 30, and 32 are connected in series in each of the
parallel paths. The examiner concludes that "it would have been obvious to one skilled in the art to use a
similar decoder to control each of the Digitally Controlled Resistors in the circuit disclosed to Hochschild
for the expected additive result of having less control lines" (Examiner's Answer, page 5). We agree that
it would have been obvious to use a digital signal and decoder as taught in Merrick to control the transistors
of Hochschild. Equally apparent is that it would have been obvious to use parallel-connected resistors as
taught by Hochschild in place of the series-connected resistors in Merrick to achieve the same result of a
variable resistance between two points. Moreover, we think that the use of parallel-connected resistors
would have been obvious even without a reference since the person of ordinary skill in the art would have
known that whatever could be done with series-connected resistors could be done with an equivalent
circuit of parallel-connected resistors. Note that Merrick describes that "[t]he internal circuit of the digitally
controlled resistance D is schematically represented by series resistors r , r and r that are respectivelyR 1 2 3
shunted by switches s , s and s ; but in actuality, the resistor connections would be much more1 2 3
complicated" (column 18, lines 57-61).
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