Electronic Components Datasheet Search
  English  ▼

Delete All


Preview PDF Download HTML

LMX1501A Datasheet(PDF) 16 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. LMX1501A
Description  PLLatinumTM 1.1 GHz Frequency Synthesizer for RF Personal Communications
Download  22 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Manufacturer  NSC [National Semiconductor (TI)]
Direct Link  http://www.national.com
Logo NSC - National Semiconductor (TI)

LMX1501A Datasheet(HTML) 16 Page - National Semiconductor (TI)

Back Button LMX1501A Datasheet HTML 12Page - National Semiconductor (TI) LMX1501A Datasheet HTML 13Page - National Semiconductor (TI) LMX1501A Datasheet HTML 14Page - National Semiconductor (TI) LMX1501A Datasheet HTML 15Page - National Semiconductor (TI) LMX1501A Datasheet HTML 16Page - National Semiconductor (TI) LMX1501A Datasheet HTML 17Page - National Semiconductor (TI) LMX1501A Datasheet HTML 18Page - National Semiconductor (TI) LMX1501A Datasheet HTML 19Page - National Semiconductor (TI) LMX1501A Datasheet HTML 20Page - National Semiconductor (TI) Next Button
Zoom Inzoom in Zoom Outzoom out
 16 / 22 page
background image
Application Information (Continued)
Therefore if we specify the loop bandwidth 0p and the
phase margin wp Equations 1 through 6 allow us to calcu-
late the two time constants T1 and T2 as shown in equa-
tions 7 and 8 A common rule of thumb is to begin your
design with a 45 phase margin
T1 e
secwp b tanwp
T2 e
0p2  T1
From the time constants T1 and T2 and the loop band-
width 0p the values for C1 R2 and C2 are obtained in
equations 9 to 11
C1 e

0p2  N
0p  T2)2
1 a (0p  T1)2
C2 e C1

R2 e
Voltage Controlled Oscillator (VCO)
Tuning Voltage constant
The fre-
quency vs voltage tuning ratio
Kw (mA)
Phase detectorcharge pump gain
constant The ratio of the current out-
put to the input phase differential
Main divider ratio Equal to RFopt fref
RFopt (MHz)
Radio Frequency output of the VCO at
which the loop filter is optimized
fref (kHz)
Frequency of the phase detector in-
puts Usually equivalent to the RF
channel spacing
In choosing the loop filter components a trade off must be
made between lock time noise stability and reference
spurs The greater the loop bandwidth the faster the lock
time will be but a large loop bandwidth could result in higher
reference spurs Wider loop bandwidths generally improve
close in phase noise but may increase integrated phase
noise depending on the reference input VCO and division
ratios used The reference spurs can be reduced by reduc-
ing the loop bandwidth or by adding more low pass filter
stages but the lock time will increase and stability will de-
crease as a result
A low pass filter section may be needed for some applica-
tions that require additional rejection of the reference side-
bands or spurs This configuration is given in
Figure 4 In
order to compensate for the added low pass section the
component values are recalculated using the new open
loop unity gain frequency The degradation of phase margin
caused by the added low pass is then mitigated by slightly
increasing C1 and C2 while slightly decreasing R2
The added attenuation from the low pass filter is
ATTEN e 20 log (2qfref  R3  C3)2 a 1
Defining the additional time constant as
T3 e R3
Then in terms of the attenuation of the reference spurs add-
ed by the low pass pole we have
T3 e
We then use the calculated value for loop bandwidth 0c in
equation 11 to determine the loop filter component values
in equations 15 – 17 0c is slightly less than 0p therefore
the frequency jump lock time will increase
T2 e
0c2  (T1 a T3)
0c e
 (T1 a T3)
(T1 a T3)2 a T1

2 a T1  T3
 (T1 a T3) 2
C1 e

0c2  N

(1 a 0c2  T22)
(1 a 0c2  T12)(1 a 0c2  T32)

Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22 

Datasheet Download

Go To PDF Page

Link URL

Privacy Policy
Does ALLDATASHEET help your business so far?  [ DONATE ] 

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Link Exchange   |   Manufacturer List
All Rights Reserved©Alldatasheet.com

Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn