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MC145193 Datasheet, PDF (19/24 Pages) Motorola, Inc – 1.1 GHZ PLL FREQUENCY SYNTHESIZER | |||
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MC145193
PHASEâLOCKED LOOP â LOWâPASS FILTER DESIGN
(A)
PDout
VCO
R
Ïn =
KÏ KVCO
NC
C
R
ζ= 2
KÏ KVCOC
N
ÏnRC
=2
1 + sRC
Z(s) = sC
NOTE:
For (A), using KÏ in amps per radian with the filterâs impedance transfer function, Z(s), maintains units of volts per radian for the detector/filter
combination. Additional sideband filtering can be accomplished by adding a capacitor Câ² across R. The corner Ïc = 1/RCâ² should be chosen
such that Ïn is not significantly affected.
R2
(B)
ÏR
R1
C
â
ÏV
A
VCO
+
R1 R2
C
Ïn =
KÏ KVCO
NCR1
ÏnR2C
ζ=
2
Assuming Gain A is very large, then:
F(s) = R2sC + 1
R1sC
NOTE:
For (B), R1 is frequently split into two series resistors; each resistor is equal to R1 divided by 2. A capacitor CC is then placed from the midpoint
to ground to further filter the error pulses. The value of CC should be such that the corner frequency of this network does not significantly
affect Ïn.
DEFINITIONS:
N = Total Division Ratio in Feedback Loop
KÏ (Phase Detector Gain) = IPDout / 2Ï amps per radian for PDout
KÏ (Phase Detector Gain) = VPD / 2Ï volts per radian for ÏV and ÏR
KVCO (VCO Transfer Function) =
2ÏâfVCO
âVVCO
radians per volt
For a nominal design starting point, the user might consider a damping factor ζ â 0.7 and a natural loop frequency Ïn â (2ÏfR / 50) where fR
is the frequency at the phase detector input. Larger Ïn values result in faster loop lock times and, for similar sideband filtering, higher fRârelated
VCO sidebands.
Either loop filter (A) or (B) is frequently followed by additional sideband filtering to further attenuate fRârelated VCO sidebands. This additional
filtering may be active or passive.
RECOMMENDED READING:
Gardner, Floyd M., Phaselock Techniques (second edition). New York, WileyâInterscience, 1979.
Manassewitsch, Vadim, Frequency Synthesizers: Theory and Design (second edition). New York, WileyâInterscience, 1980.
Blanchard, Alain, PhaseâLocked Loops: Application to Coherent Receiver Design. New York, WileyâInterscience, 1976.
Egan, William F., Frequency Synthesis by Phase Lock. New York, WileyâInterscience, 1981.
Rohde, Ulrich L., Digital PLL Frequency Synthesizers Theory and Design. Englewood Cliffs, NJ, PrenticeâHall, 1983.
Berlin, Howard M., Design of PhaseâLocked Loop Circuits, with Experiments. Indianapolis, Howard W. Sams and Co., 1978.
Kinley, Harold, The PLL Synthesizer Cookbook. Blue Ridge Summit, PA, Tab Books, 1980.
Seidman, Arthur H., Integrated Circuits Applications Handbook, Chapter 17, pp. 538â586. New York, John Wiley & Sons.
Fadrhons, Jan, âDesign and Analyze PLLs on a Programmable Calculator,â EDN. March 5, 1980.
AN535, PhaseâLocked Loop Design Fundamentals, Motorola Semiconductor Products, Inc., 1970.
AR254, PhaseâLocked Loop Design Articles, Motorola Semiconductor Products, Inc., Reprinted with permission from Electronic Design,
1987.
AN1253, An Improved PLL Design Method Without Ïn and ζ, Motorola Semiconductor Products, Inc., 1995.
MOTOROLA WIRELESS SEMICONDUCTOR
19
SOLUTIONS â RF AND IF DEVICE DATA
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