NJM567
-
-
Ver.2012-11-06
■ DESIGN FORMULAS
mVrms200V,fof%in
Cf
V
1070
~
BW
)mV0V(
C1.07R
1
f
INO
2O
IN
IN
11
O
≤−
==
where V
IN
: Input Voltage (Vrms)
C
2
: LPF Capacitor (µF)
■ PLL WORDS EXPLANATIONS
Center Frequency (f
O
)
The free-running frequency of the current controlled oscillator (CCO) in the absence of an input signal.
Detection Bandwidth (BW)
The frequency range, centered about f
O
, within which an input signal above the threshold voltage (typically 20mVrms)
will cause a logical zero state on the output. The detection bandwidth corresponds to the loop capture range.
Lock Range
The largest frequency range within which an input signal above the threshold voltage will hold a logical zero state on
the output.
Detection Band Skew
A measure of how well the detection band is centered about the center frequency, f
O
. The skew is defined as (f
max
+ f
min
- 2f
O
)/ 2f
O
where f
max
and f
min
are the frequencies corresponding to the edges of the detection band. The skew can be
reduced to zero if necessary by means of an optional centering adjustment.
Operating Instructions
Figure 1 shows a typical connection diagram for the 567. For most applications, the following three-step procedure will
be sufficient for choosing the external components R
1
, C
1
C
2
and C
3
.
Figure 1
1. Select R
1
and C
1
for the desired center frequency. For best temperature stability, R
1
should be between 2K and 20K
ohm, and the combined temperature coefficient of the R
1
C
1
product should have sufficient stability over the projected
temperature range to meet the necessary requirements.
2. Select the low pass capacitor, C
2
, by referring to the Bandwidth versus Input Signal Amplitude graph. If the input
amplitude variation is known, the appropriate value of f
O
C
2
necessary to give the desired bandwidth may be found.
Conversely, an area of operation may be selected on this graph and the input level and C
2
may be adjusted accordingly.
For example, constant bandwidth operation requires that input amplitude be above 200mVrms. The bandwidth, as noted
on the graph, is then controlled solely by the f
O
C
2
product (f
O
(Hz), C
2
(µfd)).
3. The value of C
3
is generally non-critical. C
3
sets the band edge of a low pass filter which attenuates frequencies outside
the detection band to eliminate spurious outputs. If C
3
is too small, frequencies just outside the detection band will switch the
output stage on and off at the beat frequency, or the output may pulse on and off during the turn-on transient. If C
3
is too
large, turn-on and turn-off of the output stage will be delayed until the voltage on C
3
passes the threshold voltage. (Such
delay may be desirable to avoid spurious outputs due to transient frequencies.) A typical minimum value for C
3
is 2C
2
.
