LV25700PM Datasheet, PDF (32/68 Pages) Sanyo Semicon Device – For Car Radio Single chip Tuner IC

LV25700PM
MRC
The MRC (Multipath Rejection Circuit) controls multipath noise by detecting the AC component of the IF S-meter
(AC). It consists of a noise amplifier and a detection circuit.
• Noise amplifier gain
The noise amplifier gain of the Pin 58 input is determined by the R2 and R1 resistors. (The gain can be lowered by
adding an external resistor.)
The gain can be further adjusted in four steps by the MRC Sens DAC. The high band frequency characteristics can be
adjusted by C57.
S-
meter
SA10
AC Smeter SW
27kΩ
5.3kΩ
60kΩ _{68kΩ R1}
27kΩ
30kΩ
R2
2- ₁
3+
S-meter
refrence
voltage
SA21
SA21
MRCSENS T_CONST
SNC
3+ ₁
2-
Detection
circuit
BUFF _10kΩ
80kΩ
57
S-meter sub
58
MRC_IN
56
MRC_Time
SA:D
SA21
D0-D1
MRC
Sensitivity
SA21
D2-D3
MRC Time constant
(Attack/Release Time)
C57
VCC
Recommended Setting
*
*
Description of Functions
Optimum value: According to the specifications.
Setting a smaller value enhances the sensitivity and increases the MRC amplifier
gain.
Setting a larger value worsens the sensitivity and reduces the MRC amplifier gain.
Sets the recovery time constant when the multipath countermeasure circuit
operates.
(Time from the MONO status to ST recovery)
Setting a smaller value shortens the recovery time, and setting a larger value
lengthens the recovery time.
• Detection circuit
MRC the time constant used to control separation is as
follows.
Discharge: Determined by 100Ω and C56.
Charge: Determined by I56 and C56.
* I56 can be set in four steps by the MRC time constant DAC.
VCC(PIN53)
MRC
Time
Constant
I56
DAC
500Ω
100Ω ^BUFF
MRC time constant (reference values)
DAC
C56
MRC_Time_Constant = 0
1μF
MRC_Time_Constant = 1
1μF
MRC_Time_Constant = 2
1μF
MRC_Time_Constant = 3
1μF
DAC
C56
MRC_Time_Constant = 0
0.47μF
MRC_Time_Constant = 0
1μF
MRC_Time_Constant = 0
2μF
Charge Time
360ms
515ms
890ms
4.5s
Charge Time
215ms
360ms
790ms
Discharge Time
0.63ms
0.63ms
0.63ms
0.63ms
Discharge Time
0.5ms
0.63ms
0.9ms
VCC(PIN53)
C56
58
10kΩ
80kΩ
MPX
SNC
No.A1709-32/68