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Agilent AN 346-2

Balanced Circuit Measurement with an

Impedance Analyzer/LCR Meter/Network

Analyzer

Application Note

Introduction

How a balanced circuit differs from an

unbalanced circuit

A balanced circuit has its electrical

midpoint grounded. An unbalanced

circuit, however, has one side ground-

ed. A balanced circuit is typically

used in communications equipment

because a balanced circuit has the

advantage of better spurious noise

suppression.

Measuring a balanced circuit with an

unbalanced measurement instrument

A balanced circuit cannot be directly

measured with an unbalanced meas-

urement instrument because of the

difference in their configuration.

Selecting a Balun

There are several types and brands of

balun transformers. When selecting a

balun, ensure that frequency is com-

patible with your measurement

requirements. When you measure the

impedance parameters of a balanced

circuit, you don’t have to use the

balun which has the same impedance

with the circuit under test. However,

when you measure the transmission

or reflection of it, you have to use a

balun which has the same impedance

with the circuit under test to keep

impedance matching. Table 1 shows

recommended balun transformers.

When measuring balanced circuits,

the unbalanced measuring instrument

requires a balun (balanced to unbal-

anced) transformer. A balun is a type

of impedance-matching RF trans-

former.

Figure 1 shows a balanced cable

which is an example of a balanced

circuit. The voltages of the cable’s two

conductors are at every point equal

in amplitude and opposite in phase.

Figure 2 shows an unbalanced cable

which is an example of an unbal-

anced circuit. Most measurement cir-

cuits in Agilent Technologies’ imped-

ance analyzers and LCR meters are

unbalanced.

Figure 3 shows the configuration for

measuring a balanced circuit with an

unbalanced instrument.

Note: In balanced cable measure-

ments, residual current in the balun

or the measuring instrument can

cause measurement errors. To reduce

the degree of error, perform

open/short and load compensation at

the measurement terminals of the

balun.

+V

-V

+V

+V

High

terminal

V

-V

0

Low

terminal

A

Figure 1. Balanced cable

Balanced cable

Measurement Instrument

Figure 3. Balanced cable measurement configuration

+V

0V

Figure 2. Unbalanced cable

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Measurement Configuration with a

Balun and Compensation

Impedance measurement configuration

with Agilent 4294A impedance analyzer

Figure 4 shows impedance measure-

ment configuration (1)/(2) with the

4294A.

Short standard

PN 1250-0929

Transmission measurement configuration

with a network analyzer

Figure 7 shows transmission meas-

urement configuration (3) with a net-

work analyzer.

50 Ω load standard

PN 11593A

3. Remove the connector and connect

the DUT. Measure the DUT.

Impedance measurement configuration

with the Agilent 4395A(#010)

Figure 6 shows impedance measure-

ment configuration (2) with the

4395A.

To calibrate/compensate:

Short the terminals closest to the

DUT to the signal out and to the test

port, then perform response/thru

calibration.

To calibrate/compensate for (1):

1. Perform open, short, and load

compensation at the balanced termi-

nals of the 16314-60011. Use the

furnished compensation standards of

the 16314-60011.

To calibrate/compensate:

Refer to “To calibrate/compensate for

(2)” of impedance measurement con-

figuration with 4294A impedance

analyzer.

Standards

0 Ω

PN 04191-85300

0S

PN 04191-85302

50 Ω

PN 04191-85301

Table 1. Recommended balun transformers

To calibrate/compensate for (2):

1. Assemble a female BNC connector

as shown in Figure 5.

Unb/Bal. (W)

Bandwidth

Type No.

Suppliers

50:50

100 Hz to 10 MHz

16315-60011

Agilent Technologies

50:100

100 Hz to 10 MHz

16316A

Agilent Technologies

2. Perform open, short, and load cali-

bration at the BNC connector using the

following BNC Calibration standards:

50:600

100 Hz to 3 MHz

16317A

Agilent Technologies

50:50

0.1–125 MHz

0001BB

North Hills Signal Processing

50:75

0.1–125 MHz

0101BB

North Hills Signal Processing

50:100

0.1–125 MHz

0300BB

North Hills Signal Processing

50:600

0.1–65 MHz

0700BB

North Hills Signal Processing

Agilent 4294A

75:50

0.1–100 MHz

1000BB

North Hills Signal Processing

75:75

0.1–100 MHz

1100BB

North Hills Signal Processing

75:100

0.1–100 MHz

1300BB

North Hills Signal Processing

75:600

0.1–60 MHz

1700BB

North Hills Signal Processing

Lc

Lp

Hp

Hc

Configuration (2)

Convert to 7-mm terminal

DUT

BNC(f)

Configuration (1)

APC7-N(f)

Adapter

P/N 11524A

N(m)-BNC(m)

Adapter

Shield connected

to instrument ground

Agilent 16315-60011,

16316/7A

Agilent 42942A

terminal Adapter

Connect wire and solder it to Balun

DUT

7-mm terminal

Wire

North Hills

Balun

N(m)-BNC(f)

Adapter

P/N 1250-0780

BNC(m)-Dual Banana

Jack Adapter

Shield connected

to instrument ground

DUT

Ω

UNBAL

50

Shield connected

to instrument ground

Unbalanced

16314-60011

Balanced

50

Ω

BAL

GROUND

14-mm

Figure 4. Measurement configurations with 4294A

2

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Wires

Soldering

Balun

BNC(m)-BNC(f)

Binding Post Terminal

Agilent 4395A-010

Figure 5. Assembling BNC connector

DUT

BNC(f)

7-mm N(f)

adapter

P/N 11524A

N(m)-BNC(m)

adapter

Shield connected

to instrument ground

Agilent 16315-60011,

16316/7A

Agilent 43961A

impedance test kit

Connect wire and solder it to balun

DUT

7-mm terminal

Wire

Shield connected

to instrument ground

N(m)-BNC(f)

adapter

P/N 1250-0780

BNC(m)- dual banana

jack adapter

North Hills

balun

Figure 6. Measurement configuration (2)

Instrument

Signal

out

Test

port

N or BNC

N or BNC

DUT

N(m)-BNC(m)

P/N 1250-0780

N(m)-BNC(m)

P/N 1250-0780

Agilent 16315-60011,

16316/7A

Agilent 16315-60011,

16316/7A

N(m)-BNC(m)

P/N 1250-0780

or

N(m)-BNC(m)

P/N 1250-0780

or

BNC(m) - dual banana

jack adapter

BNC(m) - dual banana

jack adapter

BNC(f)-BNC(f)

P/N 1250-0080

BNC(f)-BNC(f)

P/N 1250-0080

Wire and

soldering

Wire and

soldering

DUT

North Hills

balun

North Hills

balun

Figure 7. Measurement configuration (3)

3

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Appendix: Agilent Balun

Transformer Information

The Agilent balun transformers are

excellent interfaces for measuring

balanced components or circuits.

They can be used with unbalanced

system measurement instruments

such as impedance analyzers, LCR

meters, and/or network analyzers

(that are unbalanced system measure-

ment instruments). Agilent offers the

following balun transformers.

Figure 8. Agilent 16314-60011 and 16315-60011

Agilent 16314-60011

Agilent 16315-60011, 16316A, 16317A

The 16314-60011 can be directly

connected to a 4-terminal-pair imped-

ance analyzer or an LCR meter. High-

accuracy impedance measurements of

balanced devices can be made by

using the OPEN/SHORT/LOAD char-

acteristic. This unique feature of the

Agilent impedance analyzer and LCR

meters is performed at the binding

posts by using the furnished shorting

plate and a 50

• Reflection and transmission

measurements of balanced devices

and circuits can be measured with a

network analyzer.

• With the furnished load resistor

(50

) and short

plate, calibration can be performed

for high-accuracy measurements.

• Depending on the impedance of the

device, balanced impedance of

50

Ω

, 100

Ω

, 600

Ω

Ω

load resistor.

Ω

, 100

Ω

, or 600

Ω

can be

selected.

• Wide frequency range (100 Hz to

10 MHz (Agilent 16317A covers up

to 3 MHz))

• Recommended instruments:

• 4395A 500 MHz network/

spectrum/impedance analyzer

• 4396B 1.8 GHz network/

spectrum/impedance analyzer

• 4294A precision impedance

analyzer

• Wide frequency range

(100 Hz to 10 MHz) is covered.

• Recommended instruments:

• 4294A precision impedance

analyzer

• 4284A precision LCR meter

• 4285A precision LCR meter

• E4980A precision LCR meter

4

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Specifications

Specifications describe the instrument’s war-

ranted performance over the temperature

range of 0 to 50 °C (except where noted) and

after 30-minute warm-up time.

Table 2. Agilent balun transformers specifications

Item

16314-60011

16315-60011

16316A

16317A

Binding posts

2 signal terminals and 1 ground terminal (signal terminal spacing: 14.0 mm)

Terminal

configuration &

nominal

characteristic

impedance

Balanced port

50

Ω

50

Ω

100

Ω

600

Ω

Unbalanced

port

4 BNC connectors

1 BNC connector

50

Ω

Size (mm)

Weight (g)

Operating temperature

89(W) x 56(H) x 133 (D)

400

89(W) x 55(H) x 121 (D)

350

0 to 55

°

C

Operating humidity

Non-operation temperature

Non-operating humidity

≤

95% RH (@ 40

°

C)

-40 to +70 ° C

≤

90% RH (@ 65

°

C)

50 Ω load resistor

50 Ω load resistor

100 Ω load resistor

600 Ω load resistor

Furnished accessories

Shorting plate

Shorting plate

Shorting plate

Shorting plate

Manual

Manual

Manual

Manual

Supplemental Characteristics

Supplemental characteristics are intended

to provide information useful in applying

the instrument by giving non-warranted

performance parameters.

Table 3. Agilent Balun transformers

supplemental characteristics (at 23 ± 5 °C)

Item

16314-60011

16315-60011

16316A

16317A

Operating

frequency

100 Hz to 10 MHz

100 Hz to 3 MHz

≤ 1.0 dB (@100 kHz)

≤ 1.0 dB (relative to the insertion loss at

100 kHz)

Insertion loss

≤

1.5 dB (relative to the insertion loss at

100 kHz)

≥

±

Freq. response

≥ 10 dB (100 Hz ≤ Freq. < 300 Hz)

≥

Freq. < 300 MHz)

≥ 20 dB (300 MHz ≤ Freq. ≤ 1 MHz)

≥

10 dB (100 Hz

≤

Freq. < 7 MHz)

≥ 17 dB (7 MHz ≤ Freq. < 10 MHz)

≥ 50 dB (100 Hz ≤ Freq. < 3 MHz)

20 dB (300 Hz

≤

Return loss

15 dB (1 MHz < Freq.

≤

3MHz)

≥

Freq. < 1 MHz)

≥ 45 dB (1 MHz ≤ Freq. < 3 MHz)

50 dB (100 Hz

≤

Common mode

loss

45 dB (3 MHz

Freq. < 5 MHz)

≥

≤

≥ 40 dB (5 MHz ≤ Freq. < 10 MHz)

5

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