Appeal No. 1998-0165
Application 08/566,270
As stated in the Abstract of the reference, Anderson
discloses a frequency shift keying modulating circuit that
produces two different frequencies depending upon “the state
of a PIN switching diode in parallel with the reactive
element.” Anderson’s detailed description of the invention
discloses how the selection of frequencies is implemented.
[W]ith reference to FIG. 2, dashed block 20
shows a pair of selectable low impedance signal
path[s] from the base of transistor 17 to ground. A
high logic level from data stream 23' on data line
[40] causes transistor switch 29 to turn on
resulting in a forward biased PIN diode 27' through
bias resistors 22 and 28. With PIN diode 27'
conducting, inductor 26' is bypassed as a circuital
element and the effective low impedance signal path
is through SAW transducer 21' [sic, 21]. SAW
transducer 21' [sic, 21] has a natural stand-alone
resonant frequency of nominally 300 MHZ consistent
with the Colpitts oscillator central frequency.
Capacitor 24 is nominally 27 pF and provides for DC
blocking but has no consequential effect upon the
oscillatory loop. A low logic level on data line
23' [sic, 40] causes transistor switch 29 to turnoff
resulting in a non-conducting PIN diode 27'. With
PIN diode 27' not conducting, inductor 26' in
combination with SAW transducer [21] is the
effective low impedance signal path.
Anderson, column 3, lines 18 through 35.
Thus, the “switching device” includes transistor switch
29, which, corresponding to a high and low voltage level from
- 5 -5
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