APN1005_技术文档

APPLICATION NOTE

APN1005: A Balanced Wideband VCO

for Set-Top TV Tuner Applications

Introduction

VCO Model

Modern set-top TV DBS tuner systems require more channel

coverage, while maintaining competitive prices. This situation

creates tough design goals: to improve performance and simplify

design.

Figure 1 shows the VCO model built for open loop analysis in Libra

Series IV including the SMV1265-011 varactor model.

The circuit schematic in Figure 2 shows a pair of transistors in a

single feedback loop, connected so that collector currents would

be 180° shifted (ideally). A pair of back-to-back connected

SMV1265-011 varactors is used, rather than a single one. This

allows lower capacitance at the high-voltage range, without

changing the tuning ratio. The reason is that, apart from package

capacitance, certain mounting fringing capacitances, though

small, may strongly affect higher frequency margins. The effects

Balanced VCO configuration could be a competitive circuit

solution, since it provides the widest tuning range with practical

circuitry and layout. However, tuning margins would be further

improved by optimizing the varactor manufacturing process.

Skyworks has developed such a process to satisfy the most

ambitious wideband design goals.

of parasitic capacitances were summarized in the model as C

4

In this publication, we will address the design of the balanced-

type voltage control oscillator (VCO) based on the newly

developed varactor SMV1265-011 with the unique set of

capacitance tuning ratios and Q-quality.

and C , valued 0.4 pF each. These values may vary depending on

3

the layout of the board. Varactor DC biasing is provided through

resistors R and R , both 1 k, which may affect the phase noise,

6

8

but eliminate the need for inductive chokes. This minimizes

overall costs and the possibility of parasitic resonances — the

usual cause for frequency instability and spurs.

The phase corrector DC chokes, SRL and SRL , were modeled

1

2

as lossless inductors at 33 nH since their losses are dominated

by the 30 Ω emitter biasing resistors. DC blocking series capaci-

tances (C

and C ) are modeled as an SRC network,

SER2

SER1

including associated parasitics. Their values were optimized to

10 pF providing smooth tuning over the design band.

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APPLICATION NOTE • APN1005

Figure 1. VCO Model, Including SMV1265-011 Varactor Model

Figure 2. Transistor Pair in Single Feedback Loop

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2

APPLICATION NOTE • APN1005

The pseudo-resonator inductance is formed by microstrip trans-

In the Libra test bench shown in Figure 3 we defined an open

mission line TL , which provides necessary circuit response at

loop gain (Ku = V /V ) as the ratio of voltage phasors at the

2

OUT IN

high frequencies. This has little effect at the lower band due to

the resonator’s dominantly capacitive nature.

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 fail to converge in

some cases, and doesn’t allow clear insight into the under-

standing of VCO behavior. This property is considered an

advantage of modeling over a purely experimental study.

The function of transmission line TL is both feedback and

1

phase alignment — providing flat power response over the

tuning range.

Power output is supplied from the collectors of X or X through

1

2

the series connected resistance and DC blocking capacitance

SRC and SRC .

2

3

DC biasing for both of the transistors is supplied through a resis-

tive divider R /R /R .

In the default bench shown in Figure 4 the variables used for

more convenient tuning during performance analysis and opti-

mization are listed in a “variables and equations” component.

1

3 2

The NEC NE68119 bipolar transistors were selected to best fit

performances. Note: The circuit is very sensitive to the transistor

choice (in terms of tuning range and stability) due to wide band-

width design requirements.

For the model of NEC NE68119 we used the Gumel Poon model

of Libra IV with the coefficients provided by CEL RF & Microwave

Semiconductors Catalogue,1997-98.

Figure 3. Libra Test Bench

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APPLICATION NOTE • APN1005

Figure 4. Default Bench

SMV1265-011 SPICE Model

Figure 5 shows a SPICE model for the SMV1265-011 varactor

diode, defined for the Libra IV environment, with a description of

the parameters employed.

Figure 5. SMV1265-011 Libra IV SPICE Model

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APPLICATION NOTE • APN1005

Parameter

Description

Saturation current (with N, determine the DC characteristics of the diode)

Series resistance

Unit

A

Ω

-

Default

IS

1e-14

R

S

0

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

-

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

V

(V)

C

(pF)

JO

J

P

tance (C ) is a function of the applied reverse DC voltage (V ) and

V

R

(pF)

22.5

21.0

20.0

M

2.0

25.0

7.3

1.8

may be expressed as follows:

0–2.5

2.5–6.5

6.5–11

11–up

4.00

0.00

0.90

0.56

C

JO

68.00

14.00

1.85

C =

V

+ C

P

M

V

R

1 +

(

)

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

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APPLICATION NOTE • APN1005

100

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

10

1

R_{S_PWL}

R_SMeasured

20

0.1

0

5

10

15

20

25

30

0

5

10

15

25

30

Varactor Voltage (V)

Figure 6. SMV1265 Capacitance vs. Voltage

Varactor Voltage (V)

Figure 7. SMV1265 Resistance vs. Voltage

Figure 6 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 7, 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).

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APPLICATION NOTE • APN1005

VCO Design and Performance

Figure 8 shows the VCO schematic.

R₁₀

2.4k

V_CC1

5-8 V

R₃

C₆

1000

R₆

820

120

C₄

100

R₄

120

R₇

51

R₅

R₈

1k

820

C₅

100

T1

16 x 0.4 mm

V₁

V₂

NE68119

R₁

R₂

L₂

L₁

R₁₂

50

33

33 33 nH

33 nH

A

C₂

10

C₁

10

T2

15 x 0.7 mm

D₂

D₁

T3

R₉

1k

SMV1265

3 X 0.7 mm

R₁₁

1000

V_VAR1

C₃

100

Figure 8. VCO Schematic

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APPLICATION NOTE • APN1005

Table 3 shows the bill of materials used.

Figure 9 shows the PCB layout. The board is made of standard FR4

material 30 mils thick.

Designators

Comment

Footprint

0603

The results measured with the circuit in Figure 8, as well as the

simulated results obtained with the model in Figure 9, are shown

in Figures 10 and 11.

C

D

0603AU100JAT9 (AVX)

0603AU101JAT9 (AVX)

0603AU102JAT9 (AVX)

SMV1265-011 (Skyworks)

LL1608-F33NJ (TOKO)

CR10-330J-T (AVX)

CR10-242J-T (AVX)

CR10-102J-T (AVX)

CR10-330J-T (AVX)

CR10-121J-T (AVX)

CR10-821J-T (AVX)

CR10-510J-T (AVX)

CR10-102J-T (AVX)

NE68119 (NEC)

1

2

3

4

5

6

1

2

1

2

0603

Note: The simulated tuning curve in Figure 10 agrees with mea-

sured data, which proves the effectiveness of the above piece-wise

approximation technique.

0603

Note: In the middle of the tuning range there is disagreement

between our model and the measured results. This could be attrib-

uted to the imperfection of the model, which is highly sensitive to

the way different parasitic effects are treated. The other problem of

modeling this oscillator case was the convergence of the harmonic

balance. To facilitate convergence in this case, we kept the number

of harmonics to at least five. The sweeping frequency range is rec-

ommended to keep as close to the oscillation point as possible —

especially when analyzing the middle band area.

0603

SOD-323

0603

L

0603

R

1

0603

R

10

R

11

0603

R

0603

2

3

4

5

6

7

8

9

1

2

In Figure 11, the power response modeled at 7 V was very close to

the measurement. Higher measured power is attributed to the ana-

lyzer calibration (the calibration error of the analyzer is known to be

within a couple of decibels). The general trend of the simulated

results reflects the real VCO response almost exactly, which clearly

demonstrates the model’s effectiveness.

R

0603

R

0603

V

SOT-416

NE68119 (NEC)

Table 3. Bill of Materials

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APPLICATION NOTE • APN1005

Figure 9. PCB Layout

8

6

Measured

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

Measured @ 7 V

Simulated @ 7 V

4

2

Simulations

0

-2

-4

-6

-8

Measured @ 5 V

0

5

10

15

20

25

30

0

5

10

15

20

25

30

Varactor Voltage (V)

Figure 11. Power Response

Varactor Voltage (V)

Figure 10. Frequency Tuning

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APPLICATION NOTE • APN1005

Table 4 shows the measurement data and shows a useful tuning range

of 0.84–2.23 GHz for the applied varactor voltage from 1–27 V.

List of Available Documents

1. Balanced Wideband VCO Simulation Project Files for Libra IV.

2. Balanced Wideband VCO Circuit Schematic and PCB Layout for

Protel EDA Client, 1998 version.

V

Frequency

(GHz)

0.788

0.842

0.91

P

OUT

@ 7 V

P

OUT

@ 5 V

VAR

(V)

0

(dBm)

3. Balanced Wideband VCO Gerber Photo-plot Files

4. Detailed measurement and simulation data.

3.5

3.7

4.8

6.5

6.4

6

-8.3

-7.6

-6.1

-2.8

1

For the availability of the listed materials, please call our applica-

tions engineering staff.

2

4

1.144

1.492

1.714

1.848

1.946

2.016

2.066

2.106

2.134

2.198

2.225

2.238

6

8

1.8

10

12

14

16

18

20

25

28

30

1.2

5.2

4.8

4.4

4.3

4.4

3.7

3.5

3.4

-0.1

-0.9

-1.5

-1.8

-2.4

-3.3

-3.7

-4

Table 4. Tabulated Measurement Data

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APPLICATION NOTE • APN1005

Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided

by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the

information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to

update the materials or information and shall have no responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes.

No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or

information provided hereunder, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and

Conditions of Sale.

THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A

PARTICULAR PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY

DISCLAIMED. SKYWORKS DOES NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS

SHALL NOT BE LIABLE FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION,

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POSSIBILITY OF SUCH DAMAGE.

Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury,

death, physical or environmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any

damages resulting from such improper use or sale.

Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of

products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for

applications assistance, customer product design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications or parameters.

Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and

names are for identification purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are

incorporated by reference.

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11


型号：	APN1005
厂家：	SKYWORKS SOLUTIONS INC.
描述：	A Balanced Wideband VCO for Set-Top TV Tuner Applications 一个平衡的宽带VCO的机顶盒电视调谐器的应用电视
文件：	总11页 (文件大小：266K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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