HA12181FP Datasheet, PDF (10/21 Pages) Hitachi Semiconductor – AM Radio Noise Reduction System

HA12181FP
As the initial voltage of C509 is equal to the output voltage (VA) before the switch change, the voltage
between terminals of C509 is changed from VA to VB.
The waveform which change up to C509 becomes the output, because the voltage of C509 appears at pin 9
through the buffer.
The changed up waveform of C509 is almost linearly approximated because of the constant current change
by the feedback from the output at pin 9.
At the time of T2 when the awitches change to the normal mode (the switch position in Figure 4), the
output recovers smoothly as the voltage of C509 is VB.
However the unmatch of the wave delay time due to the pulse width or the phase circuit and the offset of
circuit make a slight step difference on the waverform at the moment of switch change.
LPF, consisting of R1 and C509 make it smooth.
The frequency characteristics, which is detriorated by LPF in the normalmode, is compensated so that it
might become flat. C509 and C510 should have the same capacity, and the tolerance must be within ±5%.
3
Phase
Circuit
HPFAmp.
R1
Buffer
9 _Out
+ _Subtraction
– _Circuit
+ Constant Current
– ^{Circuit(Subtraction}
R2
Circuit)
5
C512
68
C511
C510
10
C509
Figure 4 Waveform Processing Circuit
Rev.2, Jun. 1997, page 10 of 21