CCWN 75:14
this interval will
be proportional to the total area under the input curve. "Area"
is figured in reference to the zero voltage line: Area under a
positive voltage is positive, and area "under" a negative voltage
is considered negative. In Figure 4 the results are given of a
number of waveforms. Note that if the input goes through any
number of complete cycles, the integrator output will be zero at
the end of the time interval. This result is independent of the
phase of the input. Whenever there is a fraction of a cycle
remaining, only the area under this fractional part appears in
the integrator output, since all the other complete cycles have
equal area above and below the zero reference. The integrator
output has its largest magnitude (either positive or negative)
when the fractional portion of a cycle is equal to exactly
one-half cycle. If, as shown in Figure 1, the integrator is
driven by the output of the input mixer, the largest voltage
output from the integrator will be obtained when the mixer input
signal is zero beat and in phase with the switching signal. If
the signal is not zero beat, the integrator will receive a number
of cycles of the beat note plus a fractional remainder during its
processing interval. At the end of this interval, only the area
under the remainder will contribute to the integrator voltage
output. An important and novel feature of the CCW filter is
that only the voltage at tho outPut of the integrator at the end
of the processing interval is of interest. This voltage is
sampled by the next stage of the CCW filter which consists of a
switch, a capacitor, and a voltage follower. When the switch
closes momentarily, the capacitor charges very quickly to the
value at the output of the integrator. Then with the switch open
for the entire remainder of a processing interval, the
sample-and-hold output remains at that value. So, for the
interval following the instant of taking the sample, this circuit
is telling us what the voltage output of the integrator was at
the end of the previous interval. The final stage of the
CCW filter is a balanced modulator. All this circuit does is to
convert the d.c. voltage output of the sample/ hold circuit into
an audio tone which we can hear. The amplitude of the tone is
directly proportional to the d.c. voltage input. Now I will
explain why we have to have two signal-processing chains in the
CCW filter. In CCW, the desired signal is zero-beat with the
switching signal of the input mixer. If this signal happens to be
90 degrees out of phase with the switching signal, a single-
channel CCW filter would have no output, because the average
value of the mixer output would be zero. To get around this, and
to guarantee that the filter output will be constant regardless
of the phase of the incoming signal, we add another chain with
the switching signal to the input mixer 90 out of phase with the
first switching signal. On the output end of this second chain,
the oscillator is also 90 out of phase with respect to the
oscillator driving the first