CXA1999N Datasheet, PDF (14/19 Pages) Sony Corporation – IF Amplifier for M-ary FSK Pagers

CXA1999N
13) Principle of Quick Charge Operation
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.
BUF
CHG
C
AMP
COMP
Reference voltage
Fig. 8
14) S Curve Characteristics
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.
15) Example of Data Filter Constants
C2
R1
R2
R3
C1
C3
Parameter
bps
512
R1
22 kΩ
R2
22 kΩ
R3
22 kΩ
C1
C2
C3
0.015 µF 0.027 µF 6800 pF
fc (Hz)
350
1200
68 kΩ
68 kΩ
68 kΩ
2700 pF 4700 pF 820 pF
800
2400
39 kΩ
39 kΩ
39 kΩ
1500 pF 3300 pF 820 pF
1.7 k
3200
(6400)∗
39 kΩ
39 kΩ
39 kΩ
1200 pF 2200 pF 560 pF
2.3 k
∗ For 4 levels
Note on operation : Measures for the prevention of electrostatic breakdown should be taken to handle this IC.
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