lc72133m Sanyo Semiconductor Corporation, lc72133m Datasheet - Page 21

• Manufacturer Part Number: lc72133m
• Description: Pll Frequency Synthesizer For Electronic Tuning
• Manufacturer: Sanyo Semiconductor Corporation

2. Notes on the FMIN, AMIN, and IFIN Pins
3. Notes on IF Counting
4. DO Pin Usage Techniques
5. Power Supply Pins
6. VCO setup
7. Front end connection example
Dead Zone
The phase comparator compares fp to a reference frequency (fr) as shown in Figure 4. Although the characteristics of
this circuit (see Figure 5) are such that the output voltage is proportional to the phase difference ø (line A), a region
(the dead zone) in which it is not possible to compare small phase differences occurs in actual ICs due to internal
circuit delays and other factors (line B). A dead zone as small as possible is desirable for products that must provide
a high S/N ratio.
However, since a larger dead zone makes this circuit easier to use, a larger dead zone is appropriate for popularly-
priced products. This is because it is possible for RF signals to leak from the mixer to the VCO and modulate the
VCO in popularly-priced products in the presence of strong RF inputs. When the dead zone is narrow, the circuit
outputs correction pulses and this output can further modulate the VCO and generate beat frequencies with the RF
signal.
Coupling capacitors must be placed as close as possible to their respective pin. A capacitance of about 100 pF is
desirable. In particular, if a capacitance of 1000 pF or over is used for the IF pin, the time to reach the bias level will
increase and incorrect counting may occur due to the relationship with the wait time.
When using IF counting, always implement IF counting by having the microprocessor determine the presence of the
IF-IC SD (station detect) signal and turn on the IF counter buffer only if the SD signal is present. Schemes in which
auto-searches are performed with only IF counting are not recommended, since they can stop at points where there is
no signal due to leakage output from the IF counter buffer.
In addition to data output mode times, the DO pin can also be used to check for IF counter count completion and for
unlock detection output. Also, an input pin state can be output unchanged through the DO pin and input to the
controller.
A capacitor of at least 2000 pF must be inserted between the power supply V
This capacitor must be placed as close as possible to the V
Applications must be designed so that the VCO (local oscillator) does not stop, even if the control voltage (Vtune)
goes to 0V. If it is possible for the oscillator to stop, the application must use the control data (DLC) to temporarily
force Vtune to V
Since this product is designed with the relatively high resistance of 200 kΩ for the pull-down (on) resistors built in to
the FMIN and AMIN pins, a common AM/FM local oscillator buffer can be used as shown in the following circuit.
Programmable Divider
Reference Divider
CC
to prevent the deadlock from occuring. (Deadlock clear circuit)
SD must be used in conjunction with the IF counting time
Figure 4
fp
fr
Phase
Detector
LC72133M, 72133V
RF
LPF
DD
and V
VCO
MIX
A11940
SS
pins.
DD
and V
SS
pins for noise exclusion.
Figure 5
V
(A)
Dead Zone
ø (ns)
No. 5427-21/23
(B)
A11941