BU7861KN_08 Datasheet, PDF (7/13 Pages) Rohm – Mixer & Selector with PCM CODEC and 16bit D/A Converter

●Lowpass Correction Circuit
The headphone output terminal (either HP_X or HPX_OUT) has a built-in “lowpass correction circuit” to correct lowpass
decay, comprised of output coupling capacity and headphone impedance.
200kΩ
200kΩ
CCHPx
HP_XI
or
HPX_FB
100kΩ
-
+
CL
+
HP_X
or
HPX_OUT
OUTPUT
RL
Fig.15 Headphone Output Section Equivalent Circuit
Lowpass Cut-off Frequency
Lowpass Boost Frequency
Boost Gain
fC= 1/(2･π･CL･RL)
fBOOST = 1/(2･π･CCHPx･200kΩ)
ABOOST = 20･log((200 kΩ+1/(2･π･f･CCHPx))/100 kΩ)
(Maximum lowpass boost is 6dB.)
The constant configuration calculates the lowpass cut-off frequency fC after confirming the output coupling capacity C_L and
headphone impedance R_L used. CCHPx is determined in order for the lowpass cut-off frequency fC and lowpass boost
frequency fBOOST to roughly correspond. The recommended constants are CL = 100μF, when RL = 16Ω and CCHPx =
6800pF.
The chart below shows the frequency characteristics (calculated values) during recommended constant use.
10
5
Amp Output
0
-5
-10
After correction
-15
-20
Before correction
-25
-30
-35
-40
1
10
100
1000
10000
100000
Frequency [Hz]
Fig.16 Low pass Correction Circuit Frequency Characteristics
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