APN1001 [SKYWORKS]

Circuit Models for Plastic Packaged Microwave Diodes; 电路模型塑料封装微波二极管


型号：	APN1001
厂家：	SKYWORKS SOLUTIONS INC.
描述：	Circuit Models for Plastic Packaged Microwave Diodes 电路模型塑料封装微波二极管二极管微波
文件：	总5页 (文件大小：191K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

APPLICATION NOTE

APN1001: Circuit Models for

Plastic Packaged Microwave Diodes

Abstract

This paper reports on the measurement and establishment of

circuit models for SOT-23 and SOD-323 packaged diodes.

Results indicate that the 1.5 nH estimate for the SOT-23 is a

useful result, as is 1.2 nH for SOD-323 single packaged diodes.

It was also determined that the effective inductance of the

SOT-23 may be reduced to approximately 0.4 nH by adding a

second bond wire and modifying the microstrip line. Other lead

configurations, including parallel bond wires and common

cathode configurations, were also studied.

SOT-23

SOD-323

Figure 1. Diode Package Styles

Package Modeling

Network Analysis

Introduction

To create a high-frequency device model S-parameter, measure-

ments were taken over a wide frequency band so that resonance

and other high order effects would be included in the measure-

ments. This procedure utilizes an HP 8510C vector network

analyzer. The package under test was inserted into an Inter-

Continental Microwave test fixture as a series connected

element. This fixture uses a Thru-Reflect-Line calibration

procedure to produce accurate calibration and assures a

reference plane at the device under test.

Discrete, low-cost, surface mount semiconductor diodes are

attractive choices for UHF and microwave applications where

package parasitic may have a significant impact on performance.

The most common package styles are the SOT-23 and the

SOD-323 (Figure 1) which were neither designed nor intended

for RF service. A primary limitation to their high-frequency

performance, particularly in PIN diode shunt connected switches,

is parasitic package inductance, which limits high-frequency

isolation. The model information available from vendors of these

devices has been generally limited to estimates of inductance,

typically 1.5 nH, for single junction SOT-23 diodes. Establishing

a better model will enable circuit designers to better predict

performance and possibly give the manufacturer alternative

designs to reduce package parasitic effects.

Using this methodology, a circuit model was generated for each

of the devices as shown in Figures 2 and 3. These models pro-

duce very good correlation between the measured and simulated

performance as shown in Figure 4.

L = 0.05 nH

C = 0.01 pF

L = 0.65 nH

L = 0.7 nH

C = 0.13 pF

C = 0.015 pF

C = 0.13 pF

Figure 2. SOT-23 Circuit Model

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

200311 Rev. A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 21, 2005

APPLICATION NOTE • APN1001: CIRCUIT MODELS FOR PLASTIC PACKAGED MICROWAVE DIODES

L = 0.05 nH

C = 0.02 pF

L = 0.57 nH

C = 0.02 pF

C = 0.2 pF

Figure 3. SOD-323 Circuit Model

Simulated

Return Loss

Measured

Isolation

Simulated

Measured

Isolation

-20

Center Conductor

-20

-40

Return Loss

Ground

-40

0.1

10.0

0.1

Frequency (GHz)

Figure 4. Measurement vs. Model Simulation

of a SOT-23 Package

Figure 5. SOT-23 Validation:

Simulation vs. Measurement

Impedance Measurements

Alternative SOT-23 Designs for

Lower Inductance

To reduce the total inductance of the SOT-23 package, alternative

wire bonding schemes were studied. Figure 6 shows four

bonding wire designs considered in this study. The measured

inductance of these bonding schemes are shown on Table 1.

The HP 4291A Impedance Analyzer, an instrument based on mea-

suring the vector V/I with coverage from 1 MHz–1.8 GHz, was

also utilized to characterize inductance of the packages under

consideration. Measurements were taken on a group of PIN

diodes that were forward biased to low values of forward resis-

tance. The inductance values derived from these measurements

are shown in Table 1 and compare well with the values derived

from network analysis. The advantage of the direct impedance

measurement is the capability of a quick measurement without

the necessity of hard bonding the device to a substrate.

Single

Parallel Wires

Dual Contact

Validation of Simulated Model

Validation of the model was performed by placing the diode into a

test circuit that simulates a shunt connected switch. The test cir-

cuit was constructed using a Duriod microstrip board and the

device was placed as shown in Figure 5. This provided a different

operating environment because not only was the diode connected

differently, but the microstrip insulator had a different dielectric

constant.

Common Cathode

Figure 6. SOT-23 Configurations

The measured performance of this circuit was imported into the

circuit simulator and compared to a simulation using the circuit

model. Figure 6 shows good validation of the network analyzer

generated model.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

July 21, 2005 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • 200311 Rev. A

APPLICATION NOTE • APN1001: CIRCUIT MODELS FOR PLASTIC PACKAGED MICROWAVE DIODES

The single wire SOT-23 diode with 1.5 nH inductance will per-

transmission line as shown in Figure 7, then the effective induc-

tance is reduced to below 0.4 nH and the isolation is increased to

20 dB at 900 MHz. Figure 7 shows a plot of the measured isola-

tion of the dual bond wire package versus frequency to 4 GHz. A

plot of an inductance of 1.5 nH is shown as a reference.

form with 10.1 dB isolation at 900 MHz as a shunt connected

switch. The inductance is reduced to 1.2 nH if a parallel bond

wire is attached to the diode contact. This will increase the isola-

tion to 11.6 dB. A further reduction of inductance may be

obtained by adding a second diode chip in a common cathode

configuration. This reduces the inductance to 0.84 nH resulting in

an increase in isolation to 14.6 dB.

Table 1 shows a summary of the effective package inductance

values for the SOD-323 and SOT-23 packaged diodes with alter-

native wiring configurations using the measurement techniques

described.

Since two junctions are employed, in the common cathode alter-

native, the capacitance is doubled under reverse bias. The

consequence may be an adverse effect on insertion loss. The

inductance of the dual bond wire design is similar to the common

cathode design resulting in similar performance. But, if the

package is inserted in the microstrip circuit with a gap in the

1.5 nH

-10

-20

w/o Gap (0.83 nH)

w/Gap (0.32 nH)

Input

Output

Gap

-30

-40

-50

Ground

Frequency (GHz)

Figure 7. SOT-23 Dual Bond Wire With and Without a Gap

S-Parameter Model

(nH @ 1 GHz)

S-Parameter Validation

(nH @ 1 GHz)

HP 4291A Inductance

(nH)

Package

SOT-23

SOT-323

Configuration

Single junction

Dual no gap

1.45

1.2

1.5

0.9

0.4

1.5/1.7

Dual gap

0.5

Parallel bonds

Common cathode

Single junction

1.2

0.84

1.2

1.1

1.19

Table 1. Summary of Package Inductance Values

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

200311 Rev. A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 21, 2005

APPLICATION NOTE • APN1001: CIRCUIT MODELS FOR PLASTIC PACKAGED MICROWAVE DIODES

Conclusion

Reference

As a result of this effort, accurate and concise microwave models

are now available for commonly used, low-cost, surface mount,

SOT-23 and SOD-323 packaged diodes. The measurement

methodology utilized de-imbedding techniques valid at frequen-

cies through 10 GHz. This material will assist design engineers

to design and predict circuit performance using these popular

devices.

R.W. Waugh and D. Gustedt, “Low Cost Surface Mount Power

Limiters,” Proceedings RF EXPO WEST,

March 1992, pp. 19-40.

In addition, it was demonstrated that the inductance of the

SOT-23 may be significantly reduced by modifying both the

internal package wiring and the microstrip transmission line.

This further improves the frequency response of the package.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

July 21, 2005 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • 200311 Rev. A

APPLICATION NOTE • APN1001: CIRCUIT MODELS FOR PLASTIC PACKAGED MICROWAVE DIODES

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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

200311 Rev. A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 21, 2005

APN1001 [SKYWORKS]

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