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參數(shù)資料
| 型號： | RF2514 |
| 廠商： | RF MICRO DEVICES INC |
| 元件分類： | 通信及網(wǎng)絡(luò) |
| 英文描述： | VHF/UHF TRANSMITTER |
| 中文描述： | SPECIALTY TELECOM CIRCUIT, QCC16 |
| 封裝： | 4 X 4 MM, QFN-16 |
| 文件頁數(shù)： | 8/14頁 |
| 文件大小： | 268K |
| 代理商： | RF2514 |
Preliminary
11-34
RF2514
Rev A2 010215
11
T
that any inductance in the traces connecting the induc-
tor(s) to the VCO pins will contribute to the overall res-
onator inductance and should be subtracted from the
calculated value of L.
A parameter of the VCO that is necessary for calculat-
ing the loop filter values is the VCO sensitivity, K
VCO
(sometimes referred to as VCO gain). To determine the
VCO sensitivity, first connect the control voltage input
point (LOOP FLT pin) to ground and note the fre-
quency. (The frequency can be observed at the output
if the LD FLT pin is connected to VCC.) Then connect
the same point to the supply and again note the fre-
quency. The difference between these two frequencies
divided by the supply voltage is the VCO sensitivity
expressed in Hz/V. There is little that the designer can
do to increase the VCO sensitivity since it is largely
determined by the tuning capacitance of the on-chip
varactors. While increasing the inductor value will
increase the tuning sensitivity, it will also lower the cen-
ter frequency of the VCO's tuning range. A very small
capacitance (1pF or less) may be added across the
VCO pins, which will have the effect of lowering the
VCO center frequency and decreasing VCO sensitivity,
but this is likely to be neither necessary nor desirable in
most applications.
Should adequate centering of the VCO range be
unachievable
with
standard
options are available for proper centering. First, a two-
inductor resonator may be used with one inductor
being one standard value higher than the other. Sec-
ond, the tuning range of the VCO may be extended at
the upper limit of the control voltage by increasing the
VCO bias resistor(s). This allows the internal varactor
diodes to be slightly forward biased, further increasing
the resonator capacitance and thereby extending the
lower frequency operation. Care should be taken not to
reduce the VCO bias so much that the circuit ceases
operation at the minimum required supply voltage.
inductor
values,
two
External to the part, the designer needs to implement a
loop filter to complete the PLL. The loop filter converts
the output of the charge pump into a voltage that is
used to control the VCO. Internally, the VCO is con-
nected to the charge pump output through a 4k
resis-
tor. The loop filter is then connected in parallel with this
point at pin 12 (LOOP FLT). This limits the loop filter
topology to a second order filter usually consisting of a
shunt capacitor and a shunt series RC, as shown in the
following schematic.
The transfer function is
where the time constants are defined as
and
The frequency at which unity gain occurs is given by
This is defined as the loop bandwidth.
Once the desired phase margin (PM) and loop band-
width (
ω
LBW
) are chosen, it is possible to calculate the
time constants. These are found using the equations
and
The phase detector gain, K
PD
, is calculated by dividing
the charge pump current by 2
π
. For the RF2514, the
charge pump current is 100
μ
A.
With these known, it is then possible to determine the
values of the filter components.
V
CC
R2
C2
C1
VCO
Charge Pump
Loop Filter
F s
( )
R
2
s
τ
(
s
τ
2
s
τ
1
1
)
+
-------------------------------------------
=
τ
2
R
2
C
2
=
τ
1
R
2
C
C
2
C
1
+
C
2
------------------
=
ω
LBW
τ
1
τ
2
------------------
=
τ
1
--------------------------------------------------
)
ω
LBW
=
τ
2
ω
LBW
2
τ
1
-----------------------
=
C
1
τ
1
τ
2
----
K
K
ω
LBW
2
N
-----------------------------
1
----------------------------------------
ω
τ
ω
LBW
τ
1
2
)
2
1
(
+
=
C
2
C
1
τ
2
τ
1
----
1
–
=
R
2
τ
2
C
2
------
=
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相關(guān)代理商/技術(shù)參數(shù) |
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| RF2514_1 | 制造商:RFMD 制造商全稱:RF Micro Devices 功能描述:VHF/UHF TRANSMITTER |
| RF2514PCBA | 制造商:RFMD 制造商全稱:RF Micro Devices 功能描述:VHF/UHF TRANSMITTER |
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