HA12181FP Просмотр технического описания (PDF) - Renesas Electronics

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HA12181FP

AM Radio Noise Reduction System

Renesas Electronics 

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.2.00 Jun 15, 2005 page 9 of 19

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