STV0042 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
STV0042 Datasheet PDF : 37 Pages
| |||
STV0042/STV0056 APPLICATION NOTE
9 - ANNEXE : PLL DEMODULATOR THEORETICAL ANALYSIS
9.1 - Modelization of the STV42/56
FM Demodulator
A part from the AGC section, the FM demodulator
of the STV42/56 can be modelized as a conven-
tional PLL structure (see Figure 41).
9.2 - Frequency Response of the PLL Demodulator
In standard applications the STV42/56 is used with
the following external loop filter (left channel).
Figure 42
Figure 41
DET
KD
ωI
F(p)
Vo
VCO
K
Ko
The closed loop gain of the PLL is :
VO
ωI
(p)
=
K
1
⋅ KO
⋅
1
+
K
⋅
1
p
KO
⋅
KD
(1)
ωI = 2 π ( f(t) - fO ) in radians
VO : peak-to-peak output voltage
K : modulation depth coefficient (R05 B0-5)
Ko : VCO slope (in radians per volt)
KD : Phase detector gain (volt per radian)
Remark : The phase detector gain can be deter-
mined as follows :
KD = DETH ⋅
R33
R36
⋅ sin Φ
(left
channel)
Φ : the angle difference between incoming signal
and the VCO
The relation (1) shows that the DC gain of the PLL
is :
GDC
=
K
1
⋅ KO
Typically the STV42/56 has been designed with :
KO = 2.89 ⋅ 106 radians/volt
R33
R32
VR EF
C37
With this type of filter the PLL closed loop gain
becomes a second order low pass filter which can
be compared to the following :
VO
ωI
(p)
=
1
+
2
1
ξ
ωO
+
p
ωO
(2)
ξ : damping factor
ωO : resonnating frequency (for ξ = 0)
Comparing relations (1) and (2), the damping factor
and the resonnating frequency can be calculated
as follows :
√ ω N =
K ⋅ KO ⋅ KD
( R33 + R32 ) ⋅ C37
√ ξ =
1
+ R82
√K⋅KO⋅KD(R33+R32) C37
K ⋅ KO ⋅ KD
R33 + R32
9.3 - Lock Range and Capture Range
Lock Range : ωL = KO ⋅ K ⋅ KD
√ Capture Range : ω C ≈
ωL
( R33 + R32 ) ⋅ C37
Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility
for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result
from its use. No licence is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics.
Specifications mentioned in this publication are subject to change without noti ce. This publication supersedes and replaces all
information previously supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life
support devices or systems without express written approval of SGS-THOMSON Microelectronics.
© 1995 SGS-THOMSON Microelectronics - All Rights Reserved
Purchase of I2C Components of SGS-THOMSON Microelectronics, conveys a license under the Philips
I2C Patent. Rights to use these components in a I2C system, is granted provided that the system confo rms to
the I2C Standard Specifications as defined by Philips.
SGS-THOMSON Microelectronics GROUP OF COMPANIES
Australia - Brazil - China - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco
The Netherlands - Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A.
37/37
Share Link: 