Agilent 4395A Switching Power Supply Evaluation

Agilent 4395A 500 MHz Network/Spectrum/Impedance Analyzer

Switching Power Supply Evaluation

Product Note 4395-2

Slide 1

Switching Power Supply Evaluation with Agilent 4395A Combination Analyzer

This module introduces you to how the combination analyzer, which has the network, spectrum, and impedance functions, contributes to a switching power supply evaluation, and other applications.

Slide 2

Agenda

• Current Trend for Switching Power Supply

• Switching Power Supply Basics

• Requirements for Switching Power Supply

• Evaluation Parameters for Switching Power Supply Loop Gain Measurement Output Impedance Measurement Output Ripple and Switching Noise Measurement Component Measurement EMC Measurement

• Ordering Information

This is the agenda.

Slide 3

Switching Power Supply Evaluation with Agilent 4395A

A switching power supply evaluation method with the Agilent Technologies 4395A Network/Spectrum /Impedance Analyzer.

Slide 4

Power Supply exists everywhere

•All electronic devices have power supply

Recently, there is a strong need for electronic equipment to be small, lightweight, and have low power consumption. The power supply for such equipment must help meet the requirements described above. To satisfy these requirements, a switching power supply is often used these days. However, the switching power supply generates a noise because of its switching behavior. This means that a designer needs to consider the noise generation carefully.

[M units]

500 450 400 350 300 250 200 150 100

SwtPS Total

for PC only

1995 1996 1997 1998

Slide 5

Switching Power Supply

Market Trend

This graph shows the market trend for the switching power supply. Notice that the switching power supply market has been growing year by year. This growth rate is caused by the growth of the communication equipment and personal computers, etc.

Slide 6

Requirements for Switching Power Supply

• Small Size

Electronic device becomes smaller and smaller. To make small SwPS,

switching frequency is made higher. This causes more switching noise.

• Stability

Circuit must be stable within the environment to a certain

degree. Designing with some margin is recommended.

• Noise Reduction

Switching behavior causes noise generation. Designing with

less noise generation is necessary.

This slide shows the requirements for the switching power supply in recent years.

Slide 7

Evaluation Parameters for Switching Power Supply

SwtPS Performance Loop Gain (10 Hz – 100 kHz)

Evaluation Output Impedance (100 Hz – 100 kHz)

Ripple and Switching Noise (-10 MHz)

SwPS Regulation

EMC Evaluation (-300 MHz)

Evaluation

SwtPS Component

Selection

Component Evaluation (50 Hz – 100MHz)

Designers evaluate the switching power supply for various reasons, such as for performance evaluation, regulation evaluation, and components selection. The summary of the evaluation parameters for switching power supply are shown in this figure. As you can see from this figure, the designers need three different analyzers; network, spectrum, and impedance analyzers with the frequency range from 10 Hz to 300 MHz.

Slide 8

Switching Power Supply Evaluation with Agilent 4395A

Evaluation of Switching Power Supply requires:

• NA, SA, and ZA functions

• Frequency range 10 Hz – 300 MHz

Agilent 4395 is the BEST

instrument to evaluate

the switching power supply.

To evaluate the switching power supply requires three different analyzers (network, spectrum, and impedance analyzers), and the frequency range from the low frequency (l0 Hz) to about 300 MHz. These requirements are satisfied by the Agilent 4395A combination analyzer only. Now, we can say that the 4395A is the BEST instrument to evaluate the switching power supply.

Duty 50%

Duty 25%

Duty 75%

Low Pass

Filter

2.5

7.5

Slide 9

Switching Power Supply Basics

This figure shows a block diagram of the switching power supply. Notice that the AC input wave changes to DC output by transmitting through the noise filter, a rectifier/smoothing circuit, and a low pass filter. The feedback loop controls the output to be stable. The error amplifier is the op-amp which senses the value of the output voltage and compares it to the reference voltage. If the output voltage is too high, the inverting input of the op-amp will be more positive than the non-inverting input, and the output of the op-amp will swing negative, reducing the output of the power supply. The opposite happens if the output voltage is too low. The difference between these inputs is amplified by the error amplifier and causes the pulse width modulator to change the pulse width. The switching converter switches on/off according to the pulse width generated from the pulse width modulator.

Slide 10

Switching Power Supply Principle

This figure illustrates the switching behavior. The pulse width modulator generates the pulse where duty rate is changed according to the output of the error amplifier. The right-hand side of this figure shows the output of the pulse width generator, and the left-hand side of this figure shows the output voltage from the low pass filter. You can see that the output level of the voltage is changed by the duty rate of the pulse.

INPUT

Noise

Filter

Rectifier

Smoothing

Circuit

Low Pass

Filter

+ DC _ OUTPUT

Switching Converter

Pulse Width

Modulator

Feedback

Network

Reference

Error Amp

Switching Converter

Low Pass

Filter

Feedback

Network

Pulse Width

Moderator

Error Amp

Reference

Power

– +

Slide 11

Evaluation Parameters for Switching Power Supply

•Loop Gain Measurement

•Output Impedance Measurement

•Output Ripple and Switching Noise Measurement

•Component Measurement

•EMC Measurement

The evaluation parameters of the switching power supply will be presented from here.

Slide 12

Loop Gain Measurement

Evaluate the stability of the control system by measuring two parameters:

Phase Margin Gain Margin

Closed-loop control systems are becoming more and more common and can be found in many of today’s consumer products, as well as in very technically sophisticated products. Historically, testing control systems during the development cycle has been difficult because the desired result is the open-loop frequency response characteristic and the loop must remain closed to achieve stable operation. The open-loop characteristic, sometimes called the loop-gain characteristic, is an important measurement because it is used in defining, as well as refining, a mathematical model for the control system. It is also used to design stability compensation networks and determine stability parameters such as gain and phase margins.

Reference

Pulse Width

Modulator

Switching Converter

Low pass

Filter

Feedback

Network

+ –

R + E C

– B

C= EG C + CHG = RG E = R – B C (1+GH)=RG C = (R–B)G

= RG – BG

B = CH

R 1 + GH

C = RG – CHG Open Loop Gain

Simple Evaluation: If GH = –1 Then C/R = `

Error Amp

Slide 13

Loop Gain Measurement Control System Basics (1)

A block diagram of the switching power supply described earlier is shown again in this figure. The position of each box has been slightly changed. This figure shows that the circuit of the switching power supply can be considered as a simple feedback control system.

Slide 14

Loop Gain Measurement Control System Basics (2)

The simple feedback control system model is shown again in this figure. From this simple model we can derive the input/output relationship of a closed-loop system as C/R = G/G(1 + GH). This expression is known as the closed-loop transfer function. GH is the open-loop gain function. A simple evaluation of this equation shows that:

If GH = -1, then C/R = `

We can see that oscillations will occur if GH = -1.

Gain Margin

Gain

Phase

-180

Traditionally, Stable System is:

Gain Margin > 6 dB

Phase margin > 30 deg

Phase Margin

These parameters enable one to determine whether a system is stable or unstable.

41802A

frequency

LOAD

1:1

– IN

+ OUT

+ S

+S: Remote sensing terminal

is used to get stable output voltage

A R RF out

Agilent 4395A

Tranformer T1 is designed to have:

• Very low output impedance • Frequency response is reasonably flat

• Secondary isolated

Slide 15

Loop Gain Measurement Bode Plot

GH provides a fundamental and straightforward way to describe and understand the stability of a control system. The Bode diagram is used to enable one to determine whether a system is stable or unstable, with the concept in the form of gain and phase margin. This figure presents these two margins with the Bode diagram. The gain margin is simply the reciprocal of the gain where the openloop frequency response function’s phase is at –180°. The phase margin is equal to 180°minus the phase of the open-loop frequency response at the point where the gain is 0 dB. Traditionally, a system that has less than 30° of phase margin or less than 6 dB (a gain factor of 2.0) of gain margin is considered unacceptable.

Slide 16

Loop Gain Measurement Setup with 4395A

This figure shows the detailed equipment setup with the Agilent 4395A combination analyzer. To know the gain and phase margins of the control system in closed-loop operation, the measurement has to proceed without breaking the feedback loop. The signal from the 4395A is connected between the external output (+OUT) and the remote sensing terminals (+S). Transformer T1 is designed to have very low output impedance and reasonably flat frequency response at the measuring frequency range.

The Agilent 41802A is a 1 MΩ input adapter that

is used to monitor the ratio A/R. The R channel is used to measure the signal injected into the input of the loop, and the A channel measures the output signal of the loop. The injected signal level must be sufficiently small (ex. -20 dB) so that no part of the control loop is taken outside its linear operating range. To carry out an accurate measurement, you need the response (thru) calibration before measuring the parameter.

Slide 17

Loop Gain Measurement Example of Evaluation

This figure shows an example of the loop gain measurement with the 4395A.

Slide 18

Loop Gain Measurement

Requirements for the Instrument

To implement the loop gain measurement, a measurement instrument with the various features described in this slide is required. Notice that the 4395A satisfies all these requirements.

Requirements for Instrument

a. Covering the range from low

frequency 10 Hz to 50 kHz or more

b. Narrow bandwidth c. Small increments of frequency d. Log sweep e. Gain and phase format f. Marker function—at least 4

markers (2 markers for each margin) or delta-markers

g. Small power level

4395 (Network Analyzer)

a. Frequency range 10 Hz to

500 MHz b. IFBW: 2 Hz to 30 kHz c. NOP: 2 to 801 Frequency reso-

lution: 1 mH d. Sweep type: Log Sweep e. Format: LogMag and Phase f. Markers: 8 markers delta-

marker function g. Output Power Level: –60 dBm

to 20 dBm

Frequency

–

INPUT

LOAD

–

1 Ω

–

INPUT

LOAD

1:1

+SENSE

Converter

+OUT

– IN

+ –

41802A

RF out

Agilent 4395A

A R

–

= 1 Ω x

VA Vs

Z0=VA=

= Rs

Is Vs/Rs Vs

(ZLOAD >>Z0 → IL can be ignored.)

Slide 19

Output Impedance Measurement

• Z0 should be small (Traditionally < 1 Ω)

• To check that there is no extreme change at some frequency range

Output impedance of a power supply is the frequency response of the output voltage to a small signal current source perturbation at the power supply output.

The output impedance should be small (<1 Ω, unit:[m Ω]) to obtain good performance, and must

not have an extreme change at some frequency range, as shown in this figure. This figure also shows the conceptual implementation for the measurement. As described in the figure, output impedance is derived as Z0=Rs*Va/Vs.

Slide 20

Output Impedance Measurement Setup with 4395A

This figure shows the practical implementation of

the output impedance measurement with Rs=1 Ω.

The network analyzer measures the ratio of the output voltage perturbation to the output current perturbation. The signal from the network analyzer is transformer-coupled to the circuit, and a capacitor is used to block dc voltage from the output of the power supply. The current signal is measured

with the Agilent 41802A connected across the 1 Ω

register (RS). The R channel is used to measure the current signal, and the A channel is used to measure the output voltage perturbation. To carry out an accurate measurement, you need the response (thru) calibration before measuring the parameter.

Requirements for instrument a. Covering the range from low frequency

100 Hz or less to 100 kHz or more b. Small increments of frequency c. Log sweep d. Marker function e. Pass/Fail test

4395A (Network Analyzer) a. Frequency range

10 Hz to 500 MHz

b. NOP: 2 to 801

Frequency resolution: 1 mH c. Sweep type: Log Sweep d. Markers: 8 markers e. Built-in Limit Line Function for

Pass/Fail test

Slide 21

Output Impedance Measurement Example of Evaluation

This figure shows an example of the output impedance measurement with the 4395A.

Slide 22

Output Impedance Measurement

Requirements for the Instrument

To implement the output impedance measurement, a measurement instrument with the various features described in this slide is required. Notice that the 4395A satisfies all these requirements.

Slide 23

Output Ripple and Switching Noise Measurement

Output ripple and switching noise are:

• Specified in the specification of the communicated equipment

• Evaluated when troubleshooting for EMI and designing EMI filter, etc.

The wave of a ripple noise is described in this figure. The ripple consists of the frequency that is twice as large as the power line frequency, the switching frequency, and other irregular ripples. They appear at the output of the switching power supply. The ripple noise is expressed in peak-topeak volts in the specifications of the switching power supply. The spectral characteristics of power supplies used in communication equipment are frequently specified.

Slide 24

Output Ripple and Switching Noise Setup with Agilent 4395A

This figure shows the equipment setup for output ripple and switching noise measurement with the Agilent 4395A. The spectrum analyzer measures at the output terminal (+OUT) of the switching power supply with the Agilent 41802A.

–

+SENSE

Converter

+OUT +

–IN –

LOAD

INPUT

+ OUT

– IN

41802A

A R RF out

Agilent 4395A

Switching Frequency Style

Ripple

Ripple Noise

Input Commercial Frequency Cycle (1/2)

Commercial Frequency and harmonics twice as great as its frequency

Slide 25

Output Ripple and Switching Noise Evaluation Example (Lin Swp)

This is an evaluation example of the output ripple and switching noise measurement with linear sweep. You can see the spectrum generated from the power line frequency (60 Hz in this example), with the harmonics twice as large as its frequency (120 Hz, 240 Hz,...).

Slide 26

Output Ripple and Switching Noise Evaluation Example (Log Swp)

This is an evaluation example of the output ripple and switching noise measurement with log sweep. You can see a lot of spectrums generated from the switching frequency and its harmonics. The 4395A does not have the log sweep mode, but it can be executed with the list sweep mode and an IBASIC program.

100 kHz Span/100 Hz RBW

RBW SA

30s

4395A with stepped FFT

0.3s

 4195A

50.7s

Impedance measurement is important for components selection and circuit design

AC INPUT

Capacitor

for

Smoothing

Circuit

Transformer

Switching Converter

Pulse Width

Modulator

Photo

Coupler

Capacitor & Inductor for Low Pass Filter

DC OUTPUT

+ _

Requirements for instrument a. Covering the range from low

frequency b. Narrow bandwidth but fast speed c. Log sweep d. Marker function e. Pass/Fail Test

4395A (Spectrum Analyzer) a. Frequency range:

10 Hz to 500 MHz

b. IFBW: 1 Hz to 1 MHz

Extremely fast at narrow IFBW

c. Log Sweep

(supported by List Sweep and IBASIC) d. Markers: 8 markers e. Built-in Limit Line Function

for Pass/Fail test

Slide 27

Output Ripple and Switching Noise Requirements for the Instrument

To implement the output ripple and switching noise measurement, a measurement instrument with the various features described in this slide is required. Notice that the Agilent 4395A satisfies all these requirements.

Slide 28

Component Measurement

Switching power supply has various electronic components

The switching power supply consists of various electronic components such as capacitors, inductors, transformer, diodes, etc. Capacitors, for example, are used in the smoothing circuit, low pass filter, noise filter, etc., and must be selected carefully. The transformer and filters must be small and lightweight at high frequencies because they are to be used for communication equipment that is small and lightweight. These are the reasons why component selection and circuit design have recently become difficult and vital. The impedance analyzer is useful for designers to know the impedance characteristics of each of their components.

Requirements for the Instrument

a. Wide frequency range and

good accuracy b. Various measurement parameters c. DC Bias d. Marker function e. Equivalent Circuit Analysis f. Pass/Fail Test g. Source Level

4395A (Opt. 010 Impedance Analyzer)

a. Frequency range 100 kHz to 500 MHz

Z Accuracy: 3% (typical basic accuracy)

b. Meas. Parameter |Z|, θz, R, X, |Y|, θy,

G, B, Cp, Cs, Lp, Ls, Rs, D, Q, etc.

c. DC Bias ±40 V (20 mA max)

(Opt. 001 DC source or

External DC bias source is required) d. Markers: 8 markers e. Eqivalent Circuit Analysis Function f. Built-in Limit Line Function

for Pass/Fail test

g. Source Level: -56 dBm to +9 dBm (at DUT)

Impedance Characteristic of Aluminum Electrolytic Capacitor

Slide 29

Component Measurement Evaluation Example

Agilent 4395A can measure impedance parameters with Opt. 010.

This is an evaluation example of the impedance characteristic of an aluminum electrolytic capaci-

tor. This example displays with the IZI and θ for-

mats.

Slide 30

Component Measurement

Requirements for the Instrument

To implement the component measurement, a measurement instrument with the various features described in this slide is required. Notice that the 4395A satisfies all these requirements.

Emission

Immunity = Susceptibility

Radiated

Conducted

Slide 31

EMC Evaluation

EMC: Electro-Magnetic Compatibility

EMC EMS:Electro-Magnetic Susceptibility

EMI: Electro-Magnetic Interference

To sell products on the commercial market, customers must pass EMC requirements

All manufacturers know that in order to sell their electronic products on the commercial market, they must meet EMC (electro-magnetic compatibility) requirements. The EMC regulation consists of two parts, (electro-magnetic susceptibility) EMS and (electro-magnetic interference)EMI.

Slide 32

EMC Evaluation Two Types of EMC Measurement

This figure illustrates the relationship between radiated emissions, radiated immunity, conducted emissions, and conducted immunity. The radiated emissions testing looks for signals broadcast from the EUT (equipment under test) through space. The radiated immunity is the ability of a device or product to withstand radiated electromagnetic fields. The conducted emissions testing focuses on signals, present on the AC mains, that are generated by the EUT. The conducted immunity is the ability of a device or product to withstand electrical disturbances on power or data lines.

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0.15 MHz - 30 MHz 30 MHz - 1 GHz (JPN)

CISPR VCCI EN FCC MIL

Conducted Emission

Radiated Emission

0.15 MHz - 30 MHz 30 MHz - 1 GHz (International)

0.15 MHz - 30 MHz 30 MHz - 1 GHz (ERP)

0.45 MHz - 30 MHz 30 MHz - 40 GHz (US) 30 Hz - 100 MHz 30 Hz - 40 GHz (MIL)

• Frequency range fit for trouble-

shooting and designing at lab (10 kHz-300 MHz)

• Log frequency sweep is supported

by IBASIC

• Setting limit line based on the type

of the regulation

Radiated EMI Evaluation

Agilent 4395A

Close-Field Probe

Circuit Under Test

There are some regulations with ≥ 1 GHz upper limit. But for troubleshooting at lab, approx. 300 MHz is enough for designers.

Slide 33

EMC Evaluation

Regulations and EMI Frequency Range

One of the most important standard setting organizations for commercial EMC standards is CISPR. It is an international group with members from many different countries that develops recommended EMC test limits and test procedures. The CISPR has no regulatory authority of its own. It is up to the regulatory agencies of each country to adopt their own EMC requirements. Most countries, however, use the CISPR standards, with some modifications, as the basis for their own national regulations, such as Voluntary Control Council for Interference by ITE (VCCI), Federal Communications Commission (FCC), and European Norms (ENs). For example, a product must pass the applicable FCC EMI requirements to be legally sold in the United States. To achieve this certification, EMI test data must be submitted to the FCC. The manufacturers must place an identification label on their product and a notice in the operating manual stating that the product meets the FCC requirements. Notice that the radiated emission at higher frequency is over 1 GHz. But for troubleshooting at R&D or in the laboratory, designers require up to about 300 MHz.

Slide 34

EMC Evaluation with Agilent 4395A

Troubleshooting by Designers (1)

Full EMC evaluation requires a special facility and test site. And in all cases, it is located far from the place where the designers are developing their products. This means that the designers cannot do very many EMC evaluations at the site during the development cycle. But waiting until the end of the development cycle to find out whether or not a product passes regulatory agency requirements can be a gamble in cost and time. The best option for designers is to be able to perform an EMC test during the product development cycle at any time they want to. This figure shows an example of the radiated EMI evaluation setup for designers at a laboratory. A close-field probe is connected with the 4395A. Sometimes an amplifier is connected between the 4395A and the close-field probe to make radiated emission measurements more sensitive. As described in the previous slide, the frequency range in EMC testing is up to about 300 MHz. The 4395A is useful to evaluate EMC with the limit line function and log sweep (implemented by list sweep feature and IBASIC program).

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Conducted EMI Evaluation

4395A

Transient

Limiter

LISN

Line Impedance Stabilization Network

Power Line

Circuit Under Test

Slide 35

EMC Evaluation with Agilent 4395A Troubleshooting by Designers (2)

This figure shows an example of the conducted EMI evaluation setup for designers at a laboratory. A line impedance stabilization network (LISN) and transient limiter are connected with the Agilent 4395A. The transient limiter protects the spectrum analyzer input from damage caused by high-level transients from the LISN during EMI testing for conducted emissions.

Slide 36

EMC Evaluation with Agilent 4395A Evaluation Example

This figure shows an example of the EMC evaluation with the limit line function of the 4395A.

• Configuration Agilent 4395A Network/Spectrum/Impedance Analyzer

Opt. 010 Add Impedance Measurement Function 43961 RF Impedance Test Kit (add test fixture listed below) 16191A Side Electrode SMD Test Fixture 16192A Parallel Electrode SMD Test Fixture 16197A Bottom Electrode SMD Test Fixture 16092A Spring Clip Test Fixture

Agilent 41802A 1 MΩ Input Adapter Agilent 10441A 10: 1 Probe (x2) Agilent 87512A/B 50/75 Ω Transmission Reflection Test Kits

• Literature 4395A/96B Awareness Brochure 5965-9374E 4395A Technical Data 5965-9340E 4395A Switching Power Supply Evaluation 5968-7274E

Requirements for Instrument

a. Covering the range up to about

300 MHz b. Narrow bandwidth but fast speed c. Log sweep d. Marker function e. Pass/Fail Test

4395A (Spectrum Analyzer)

a. Frequency range:

10 Hz to 500 MHz

b. IFBW: 1 Hz to 1 MHz

Exremely fast at narrow IFBW

c. Log sweep (supported by List

Sweep and IBasic) d. Markers: 8 markers e. Built-in Limit Line Function for

Pass/Fail test

Slide 37

EMC Evaluation

Requirements for the Instrument

To implement EMC evaluations, a measurement instrument with the various features as described in this slide is required.

Slide 38

Ordering Information

This slide shows the configuration list for switching power supply evaluation and the available literature for the 4395A combination analyzer.

100 kHz Span/100 Hz RBW

RBW SA

Analog 4395A with step ped FFT

0.3s

30s

HP 4195A

50.7s

The 4395A offers the following essential features:

• It has NA, SA, and ZA functions,

• Its frequency range is 10Hz – 300MHz, and

• Satisfies all requirements for each evaluation

Other benefits compared to analyzers with one function (NA or SA):

User friendly IF Shorter time to create a program Reduces maintenance time and cost Saves bench space

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Product specifications and descriptions in this document subject to change without notice.

Loop Gain

Output Z

EMC

Ripple & Switching Noise

Slide 39

Switching Power Supply Evaluation with Agilent 4395A Summary

The 4395A satisfies all requirements for every evaluation and also has more benefits for designers compared with analyzers that have only one function (NA or SA). We can offer that the Agilent 4395A is the best instrument for evaluating the switching power supply.

Agilent 4395A Switching Power Supply Evaluation

Specifications and Main Features

Frequently Asked Questions

User Manual