CXA3117N Datasheet, PDF (16/30 Pages) Sony Corporation – IF Amplifier for M-ary FSK Pagers

CXA3117N
12)-3. Offset Amount and Threshold Value
Immediately after power-on when the REF capacitor is not charged with the correction voltage, if the input
frequency has an offset, some time is required to correct this offset. In addition, the times required to obtain
2-level and 4-level data differ according to the offset amount.
a) 2-level signals
In the case of 2-level signals, correct data is obtained when the offset amount is smaller than the detector
output amplitude. This is 75mV or less when the detector output level is 150mVp-p which corresponds to
within ±4.8kHz when converted to a frequency by the S curve. Thus, 2-level data is obtained without an
operation point correction time lag when the frequency offset is within ±4.8kHz.
NRZ threshold
value offset
b) 4-level signals
In the case of 4-level signals, correct data is obtained when the offset amount is less than 1/3 of the
detector output amplitude (during ±4.8kHz DEV). This is 25mV or less when the detector output level is
150mVp-p which corresponds to ±1.6kHz or less when converted to a frequency by the S curve, . Thus, 4-
level data is obtained without an operation point correction time lag when the frequency offset is within
±1.6kHz.
Level comparator threshold value 1
NRZ threshold
value offset
Level comparator threshold value 2
As shown above, 4-level signals have an allowable offset range 1/3 that of 2-level signals. When the offset
exceeds this allowable range, time is required to determine the operation point and obtain correct data
through feedback. Also, even if the offset is within the allowable range, the output pulse duty changes until
the offset is 0.
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