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參數(shù)資料
| 型號(hào)： | AN1207 |
| 廠商： | 飛思卡爾半導(dǎo)體(中國(guó))有限公司 |
| 英文描述： | THE MC145170 in Basic HF and VHF Oscillators |
| 中文描述： | 在基本高頻和甚高頻MC145170振蕩器 |
| 文件頁(yè)數(shù)： | 4/6頁(yè) |
| 文件大?。?/td> | 267K |
| 代理商： | AN1207 |
AN1207
4
MOTOROLA
Figure 5. VHF Synthesizer
–
+
R1/2
R1/2
R1/2
R1/2
4 x 5.6 k
2 x 1500 pF
2 x MV2115
24 k
4700 pF
+ 12 V
CC
CC
1 k
TEST POINT
(LOCK DETECT)
4700 pF
24 k
LF351
R14
10 k
20 nH
0.1
μ
F
390 pF
C5
1000 pF
MC1648
MC145170
1 M
1 MHz
Y1
20 pF
20 pF
100 pF
OUTPUT
DATA OUT
CLK
EN
DATA IN
1
8
9
16
1
7
8
14
+ 5 V
+ 5 V
+ 5 V
midpoints to ground to further filter the reference sidebands.
The value of CC is chosen so that the corner frequency of this
added network does not significantly affect the original loop
bandwidth
ω
B.
The rule of thumb for an initial value is CC = 4 / ( R1
ω
RC),
where
ω
RC is the filter cutoff frequency. A good value is to
choose
ω
RC to be 10 x
ω
B, so as to not significantly impact the
original filter.
ω
B =
ω
n
1 + 2
ζ
2 + 2 + 4
ζ
2 + 4
ζ
4
(8)
= 12,566
1+(2)(0.707)2+ 2+(4)(0.707)2+ (4)(0.707)4
= 25,860 rad/s
(9)
ω
RC = 10
ω
B = (10)(25,860) = 258,600 rad/s
CC =
4
R1
ω
RC
(10)
(11.23 k
)(258,600 rad/s)
=
= 1377 pF
≈
1500 pF
4
There is also a filter formed at the input to the VCO. Again,
this should be selected to ensure that it does not significantly
affect the loop bandwidth.
For this example, the filter is domi-
nated by R14 with C5. The capacitance of the varactors (in
series with the rest of the circuit) is much smaller than C5 and
can therefore be neglected for this calculation.
As above, let
ω
RC = 258,600 rad/s be the cutoff of this filter.
R14 is chosen to be 10 k
. Therefore,
1
ω
RCR14
(258,600)(10 k
)
C5 =
(11)
=
= 387 pF
≈
390 pF
1
THE VARACTOR
The MV2115 was selected for its tuning ratio of 2.6 to 1.
The capacitance can be changed from 49.1 pF to 127.7 pF
over a reverse bias swing of 2 to 30 volts. Contact your Moto-
rola representative for information regarding the MV2115 va-
ractor diode.
For example, three parameters are considered.
CT = Nominal capacitance
CR = Capacitance ratio
fR = Frequency ratio
CR=Cvmin
Cvmax
(12)
Vmax
Vmin
=
ρ
where
ρ
= the capacitance exponent
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.
ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005
A
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