APN1006 [SKYWORKS]
A Colpitts VCO for Wideband (0.95–2.15 GHz) Set-Top TV Tuner Applications; 考毕兹VCO的宽带（ 0.95-2.15千兆赫）机顶盒电视调谐器的应用
| 型号： | APN1006 |
| 厂家： | 
SKYWORKS SOLUTIONS INC. |
| 描述： | A Colpitts VCO for Wideband (0.95–2.15 GHz) Set-Top TV Tuner Applications |
| 文件： | 总8页 (文件大小：252K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
APPLICATION NOTE
APN1006: A Colpitts VCO for Wideband
(0.95–2.15 GHz) Set-Top TV Tuner Applications
rates the SMV1265-011 varactor diode. This varactor diode was
Introduction
specifically developed at Skyworks for this application. The VCO
design, based on Libra Series IV simulation, shows good correla-
tion between measured and simulated performance. This
application note includes a board layout and materials list.
Modern set-top DBS TV tuners require high-performance, broad-
band voltage control oscillator (VCO) designs at a competitive
cost. To meet these goals, design engineers are challenged to
create high-performance, low-cost VCOs.
The Colpitts oscillator is a traditional design used for many VCO
applications. Designing a broadband Colpitts oscillator with cov-
erage from 1–2 GHz requires the selection and interaction of an
appropriate varactor diode for its resonator. This application note
describes the design of a broadband Colpitts VCO that incorpo-
VCO Model
Figure 1 shows the VCO model built for open loop analysis in Libra
Series IV.
Figure 1. VCO Model Built for Open Loop Analysis in Libra Series IV
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1
APPLICATION NOTE • APN1006
This circuit schematic, which is a simple Colpitts structure, uses
a series back-to-back connection of two SMV1265-011 varactors
instead of a single varactor. This connection allows lower capaci-
tance at high voltages, while maintaining the tuning ratio of a
single varactor. The back-to-back varactor connection also helps
reduce distortion and the effect of fringing and mounting capaci-
tances. These parasitic capacitances are included in the model as
The NEC NE68533 transistor was selected to fit the required
bandwidth performance. Note: The circuit is very sensitive to the
transistor choice (tuning range and stability) due to the wide
bandwidth requirement. The output is supplied from the emitter
load resistance (RL ) through the 2 pF coupling capacitor, mod-
1
eled as a series SLC component.
1
The microstrip line (TL ) simulates the design layout which may
1
C , valued at 0.6 pF. This value may change depending on the
5
be incorporated in the resonator.
layout of the board.
Figure 2 shows the Libra test bench. In the test bench, we define
DC bias is provided through resistors R and R , both 3 kΩ,
1
4
an open loop gain (Ku = V /V ) as a ratio of voltage phasors at
OUT IN
which may affect phase noise, but allows the exclusion of
chokes. This reduces costs and the possibility of parasitic
resonances — the common cause of spurious responses and
frequency instability.
input and output ports of an OSCTEST component. Defining the
oscillation point requires the balancing of input (loop) power to
provide zero gain for a zero loop phase shift. Once the oscillation
point is defined, the frequency and output power can be mea-
sured. Use of the OSCTEST2 component for the close loop
analysis is not recommended, since it may not converge in some
cases, and doesn’t allow clear insight into understanding the VCO
behavior. These properties are considered an advantage of mod-
eling over a purely experimental study.
The resonator inductance was modeled as a lossy inductor (with
Q = 25 at 100 MHz) in parallel with a capacitance of 0.25 pF.
This is typical for a multilayer inductor of style 0603 (60 x 30 mil)
footprint (TOKO Coils and Filters catalog). The inductor value of
5.6 nH was optimized to fit the desired 1–2 GHz frequency band.
The DC blocking series capacitance (C ) was modeled as an
SER
SRC network, including associated parasitics; it was selected at
1000 pF to avoid affecting the resonator (Q).
The Colpitts feedback capacitances (C
= 1 pF and C
=
DIV2
DIV1
1.62 pF) were optimized to provide a flat power response over
the tuning range. These values may also be re-optimized for
phase noise if required.
Figure 2. Libra Test Bench
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APPLICATION NOTE • APN1006
Figure 3. Default Test Bench
Figure 3 shows the default bench. The variables used for more
convenient tuning during performance analysis and optimization
are listed in a “variables and equations” component.
SMV1265-011 SPICE Model
Figure 4 shows a SPICE model for the SMV1265-011 varactor
diode, defined for the Libra IV environment, with a description of
the parameters employed.
Figure 4. SMV1265-011 Libra IV SPICE Model
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200316 Rev. A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 21, 2005
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APPLICATION NOTE • APN1006
Parameter
Description
Unit
A
Ω
-
Default
IS
R
Saturation current (with N, determine the DC characteristics of the diode)
1e-14
Series resistance
0
S
N
Emission coefficient (with IS, determines the DC characteristics of the diode)
Transit time
1
TT
S
F
0
C
JO
Zero-bias junction capacitance (with V and M, defines nonlinear junction capacitance of the diode)
0
J
V
J
Junction potential (with V and M, defines nonlinear junction capacitance of the diode)
V
1
J
M
Grading coefficient (with V and M, defines nonlinear junction capacitance of the diode)
-
0.5
J
E
Energy gap (with XTI, helps define the dependence of IS on temperature)
EV
-
1.11
G
XTI
KF
AF
FC
Saturation current temperature exponent (with E , helps define the dependence of IS on temperature)
3
G
Flicker noise coefficient
-
0
Flicker noise exponent
-
1
Forward-bias depletion capacitance coefficient
Reverse breakdown voltage
-
0.5
B
V
Infinity
V
I
Current at reverse breakdown voltage
Recombination current parameter
Emission coefficient for ISR
A
A
-
1e-3
BV
ISR
NR
0
2
IKF
High injection knee current
A
-
Infinity
NBV
IBVL
NBVL
Reverse breakdown ideality factor
Low-level reverse breakdown knee current
Low-level reverse breakdown ideality factor
Nominal ambient temperature at which these model parameters were derived
Flicker noise frequency exponent
1
0
A
-
1
T
NOM
°C
27
1
FFE
Table 1. Silicon Varactor Diode Default Values
Table 1 describes the model parameters. It shows default values
appropriate for silicon varactor diodes which may be used by the
Libra IV simulator.
whole range of the usable varactor voltages is segmented into a
number of subranges each with a unique set of the V , M, C ,
J
JO
and C parameters as given in the Table 2.
P
According to the SPICE model in Figure 4, the varactor capaci-
Voltage Range
(V)
C
M
V
(V)
C
P
(pF)
JO
J
tance (C ) is a function of the applied reverse DC voltage (V ) and
V
R
(pF)
22.5
21
may be expressed as follows:
0–2.5
2.5–6.5
6.5–11
11–up
2
4
0
C
JO
25
7.3
1.8
68
0
C =
V
+ C
P
M
20
14
0.9
0.56
V
R
1 +
(
)
20
1.85
V
J
Table 2. Varactor Voltages
This equation is a mathematical expression of the capacitance
characteristic. The model is accurate for abrupt junction varactors
(SMV1400 series); however, the model is less accurate for hyper-
abrupt junction varactors because the coefficients are dependent
on the applied voltage. To make the equation fit the hyperabrupt
performances for the SMV1265-011, a piece-wise approach was
These subranges are made to overlap each other. Thus, if a rea-
sonable RF swing (one that is appropriate in a practical VCO
case) exceeds limits of the subrange, the C function described
V
by the current subrange will still fit in the original curve.
employed. Here the coefficients (V , M, C , and C ) are made
J
JO
P
piece-wise functions of the varactor DC voltage applied. Thus, the
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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APPLICATION NOTE • APN1006
100
10
1
1.0
0.8
0.6
0.4
0.2
0
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
Approximation
Measured
RS_PWL
RS Measured
0.1
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Varactor Voltage (V)
Figure 5. SMV1265 Capacitance vs. Voltage
Varactor Voltage (V)
Figure 6. SMV1265 Resistance vs. Voltage
Figure 5 demonstrates the quality of the piece-wise fitting
approach.
Since the epitaxial layer for this kind of hyperabrupt varactor has
relatively high resistivity, the series resistance is strongly depen-
dent on the reverse voltage applied to varactor junction. The
Special consideration was given to the fit at the lowest capaci-
tance range (high-voltage area) since it dramatically affects the
upper frequency limit of the VCO.
value of series resistance (R ) measured at 500 MHz is shown in
S
Figure 6, with a piece-wise approximation of R also given.
S
The piece-wise function may be used as follows:
To incorporate this function into Libra, the pwl() built-in function
was used in the “variables” component of the schematic bench.
R = pwl (V 0 2.4 3 2.4 4 2.3 5 2.2 6 2 7 1.85 8 1.76 9
S
VAR
1.7 10 1.65 11 1.61 12 1.5 40 1.5)
M = pwl (V 0 2 2.5 2 2.500009 25 6.5 25 6.50009 7.3 11
VAR
7.3 11.0009 1.8 40 1.8)
Note: The pwl() function in Libra IV is defined for the evaluation of
harmonic balance parameters rather than variables. Therefore,
although series resistance was defined as dependent on reverse
voltage, for harmonic balance it remains parametric and linear.
The same applies to capacitance, which remains the same as in
V = pwl (V 0 4 2.5 4 2.500009 68 6.5 68 6.50009 14 11
J
VAR
14 11.0009 1.85 40 1.85)
C = pwl (V 0 0 2.5 0 2.500009 0 6.5 0 6.50009 0.9 11
P
VAR
0.9 11.0009 0.56 40 0.56)
the original diode model, but its coefficients (V , M, C , and C )
J
JO
P
C
JO
= pwl (V 0 22.5 2.5 22.5 2.500009 21 6.5 21 6.50009
become parametric functions of the reverse voltage.
VAR
20 11 20 11.0009 20 40 20)*1012
Note: While C is given in picofarads, C is given in farads to
P
GO
comply with the default nominations in Libra. (For more details
regarding pwl() function see Circuit Network Items, Variables and
Equations, Series IV Manuals, p. 19–15).
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
200316 Rev. A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 21, 2005
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APPLICATION NOTE • APN1006
Table 3 shows the bill of materials used.
VCO Design Materials, Layout, and Performance
Figure 7 shows the VCO circuit diagram.
Designator
Part Type
Footprint
0603
C
C
C
C
C
C
D
0603AU561JAT9 (AVX)
0603AU2R0JAT9 (AVX)
0603AU561JAT9 (AVX)
0603AU201JAT9 (AVX)
0603AU1R0JAT9 (AVX)
0603AU1R6JAT9 (AVX)
NE68519 (NEC)
1
2
3
4
5
6
1
1
0603
0603
VCC = 5 V
Icc = 9 mA
3.3 k
NE68519
0603
0603
560 p
9.1 k
VTUNE
320 x 30 mils
5.6 nH
0603
SOT-419
0603
1 p
SMV1265-011
L
LL1608-F5N6S (TOKO)
CR10-332J-T (AVX)
2 p
3 k
3 k
SMV1265-011
R
R
R
R
R
0603
1
2
3
4
5
1
2
RF Output
CR10-912J-T (AVX)
0603
1.62 p
300 p
CR10-201J-T (AVX)
0603
200
CR10-302J-T (AVX)
0603
CR10-302J-T (AVX)
0603
Figure 7. VCO Circuit Diagram
V
V
SMV1265-011 (Skyworks)
SMV1265-011 ( Skyworks)
SOD-323
SOD-323
Table 3. Bill of Materials
Figure 8 shows the PCB layout. The board is made of standard FR4
material 60 mils thick.
720 MIL
Figure 8. PCB Layout
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APPLICATION NOTE • APN1006
Figure 9 shows both the measured performance of this circuit and
the simulated results, obtained with the above model. The simu-
lated tuning curve (frequency vs. voltage) is in excellent agreement
with measured data, proving the effectiveness of the piece-wise
approximation technique. The measured power response, shows
some differences from its simulation, but is within the same range.
A possible reason for the discrepancy could be the effect of higher
harmonics. To simulate this would require significantly more com-
plicated modeling of the components, board parasitics, and
discontinuities. However, for most engineering purposes, the circuit
performance prediction indicated here should be satisfactory.
List of Available Documents
1. Colpitts Wideband VCO Simulation Project Files
for Libra IV.
2. Colpitts Wideband VCO Circuit Schematic and PCB Layout for
Protel EDA Client, 1998 version.
3. Colpitts Wideband VCO Gerber Photo-plot Files
4. A Colpitts VCO for Wideband (0.95–2.15 GHz)
Set-Top TV Tuner Applications. (Current Document).
5. Detailed measurement and simulation data.
For the availability of the listed materials, please call our applica-
tions engineering staff.
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
7
6
5
4
3
2
1
0
POUT_MODEL
POUT_EXP
FEXP
© Skyworks Solutions, Inc., 1999. All rights reserved.
FMODEL
0
5
10
15
20
25
30
Varactor Voltage (V)
Figure 9. Measured and Simulated
Frequency vs. Varactor Voltage
Table 4 shows tabulated measurement data. In voltage ranges of 1–27
V, the usable frequency coverage was estimated from 0.98–2.15 GHz.
V
Frequency
(GHz)
0.95
P
OUT
VAR
(V)
0.5
1
(dBm)
5.7
5.5
5.4
4.7
3.2
5.2
4.9
5
0.974
1.018
1.184
1.68
2
4
8
12
14
18
22
25
30
1.886
1.932
2.008
2.076
2.12
3.9
3.5
2.2
2.188
Table 4. Tabulated Measurement Data
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APPLICATION NOTE • APN1006
Copyright © 2002, 2003, 2004, 2005, Skyworks Solutions, Inc. All Rights Reserved.
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information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to
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