CXA1999 SONY [Sony Corporation], CXA1999 Datasheet - Page 14

• Manufacturer Part Number: CXA1999
• Description: IF Amplifier for M-ary FSK Pagers
• Manufacturer: SONY [Sony Corporation]

13) Principle of Quick Charge Operation
14) S Curve Characteristics
15) Example of Data Filter Constants
Note on operation : Measures for the prevention of electrostatic breakdown should be taken to handle this IC.
For 4 levels
bps
(6400)
1200
2400
3200
Parameter
BUF in Fig. 8 is the detector buffer amplifier, and AMP is an operational amplifier to construct an LPF.
COMP is the level comparator or the NRZ comparator. The CXA1999N has a feedback loop from the
comparator input to the input circuit of the detector output buffer. This equalizes the average value of the
comparator input voltage to the reference voltage, with the quick charge circuit of CHG being set in the
feedback loop. Switching the current of the quick charge circuit enables reduction of the rise time.
In this block, CHG is a comparator which compares input voltages and outputs a current based on this
comparison. The current on CHG is switched between high and low at Pin 14. When the power is turned
on, switch the current to high to increase the charge current at C in Fig. 8 and shorten the time constant.
During steady-state reception mode, switch the current to low, lengthening the charge time constant and
allowing for stable data retrieval.
Even if the IF IN input signal frequency is deviated, the feedback is applied to the DET OUT operating
point so as to match it to the comparator reference voltage by the quick charge operation shown in Fig. 8.
Therefore, this feedback must be halted in order to evaluate the S curve characteristics.
To execute the evaluation, measure the average voltage on Pin 12 first and input this voltage to Pin 7 from
the external power supply.
512
22 kΩ
68 kΩ
39 kΩ
39 kΩ
R
1
C
BUF
22 kΩ
68 kΩ
39 kΩ
39 kΩ
R
2
CHG
R
1
22 kΩ
68 kΩ
39 kΩ
39 kΩ
R
C
R
1
3
2
—14—
Fig. 8
R
3
0.015 µF
2700 pF
1500 pF
1200 pF
C
C
1
3
C
AMP
2
0.027 µF
4700 pF
3300 pF
2200 pF
C
2
Reference voltage
6800 pF
820 pF
820 pF
560 pF
COMP
C
3
fc (Hz)
1.7 k
2.3 k
350
800
CXA1999N