1
C
1R1
214
Communication ICs BA1604 / BA1604F
Measurement circuit Application example
Attached components
(1) C
1 and R1 : Setting f0
The center frequency (f0) is determined by the resistor R1
between Pins 5 and 6, and the capacitor C1 between Pin
6 and the ground. The constants at this point are deter-
mined as follows :
f
0 (kHz) (C : µ F, R : kΩ)
A rectangular-wave voltage is output at Pin 5; the peak-
to-peak amplitude is between V
CC and 1.4 V, and the av-
erage DC value is V
CC / 2. This pin can drive a load resis-
tance of up to 1kΩ. (The recommended value for R
1,
however, is from 2kΩ to 20kΩ.)
A 1V peak-to-peak exponential function triangular wave
with an average DC voltage level of V
CC / 2 is output at Pin
6. Since loading this pin adversely affects both the duty
cycle and the temperature stability of the oscillator, it
must only be connected to a high-impedance load.
(2) C
2 : Loop filter
Connected between Pin 2 and the ground, C
2 functions
as a low pass filter for the PLL circuit, and the time
constant is determined by T
2 = R2C2 (R2 is the internal im-
pedance for Pin 2, at 10 kΩ). The value of C
2 also deter-
mines the detection bandwidth. The voltage at Pin 2 va-
ries linearly at 20mV / % of f
0 over the range 0.95 f0 to
1.05 f
0.
(3) C
3 : Output filter
Capacitor C
3, connected between Pin 1 and the ground,
is used as a low pass filter to suppress out-of-band sig-
nals. The time constant T
3 is determined by T3 = R3C3 (R3
is the internal impedance for Pin 1, at 4.7kΩ).
To prevent false detection of spurious signals, it is recom-
mended that C
3 2C2. If C3 is made too large, howev-
er, this will increase the time required for voltage changes
at Pin 1 to reach the threshold of the phase detector, thus
slowing the response time.
(4) C
4 : Input coupling capacitor
(5) C
5 : Power supply filter capacitor
Input and output pins
(1) Input : Pin 3
The input signal is applied through a coupling capacitor
to Pin 3. Internal circuits set this pin to a DC potential of
2V with respect to the ground. The input impedance is
approximately 20kΩ.
(2) Output : Pin 8
The output logic section has an internal power transistor
with its collector connected to Pin 8. The load is con-
nected between Pin 8 and V
CC. The transistor saturates
when an in-band input signal is received, dropping the
potential at Pin 8 to less than 1V (0.6V Typ.). The output
can also drive a load connected to a separate supply volt-
age of up to 20V.
