Agilent VI emulation mode of programmable output resistance function B2960-90042 [1] Datasheet

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Page 1

Agilent B2961A/B2962A Low Noise Power Source

Programmable Output Resistance



Using VI Emulation Mode

Agilent Technologies

Page 2

Notices

No part of this manual may be reproduced in any form or by any means (including electronic storage and retrieval or translation into a foreign language) without prior agreement and written consent from Agilent Technologies, Inc. as governed by United States and international copyright laws.

Manual Part Number

B2960-90042

Edition

Edition 1, October 2012 

Agilent Technologies 5301 Stevens Creek Blvd  Santa Clara, CA 95051 USA

Warranty

The material contained in this document is provided “as is,” and is subject to being changed, without notice, in future editions. Further, to the maximum extent permitted by applicable law, Agilent disclaims all warranties, either express or implied, with regard to this manual and any information contained herein, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. Agilent shall not be liable for errors or for incidental or consequential damages in connection with the furnishing, use, or performance of this document or of any information contained herein. Should Agilent and the user have a separate written agreement with warranty terms covering the material in this document that conflict with these terms, the warranty terms in the separate agreement shall control.

(June 1995), or as a “commercial item” as defined in FAR 2.101(a) or as “Restricted computer software” as defined in FAR

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52.227-19(c)(1-2) (June 1987). U.S. Government users will receive no greater than Limited Rights as defined in FAR 52.227-14 (June 1987) or DFAR 252.227-7015 (b)(2) (November 1995), as applicable in any technical data.

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Contents

1. Introduction ........................................................................................................................................ 4

2. VI Emulation Mode ........................................................................................................................... 5

Emulation table and PWL interpolation ......................................................................................... 6

Primary source mode and shape of I-V characteristics ............................................................... 6

V/I mode setting ................................................................................................................................ 8

Emulation table setting example ................................................................................................... 10

Combination of V/I mode ............................................................................................................... 11

Available Rs/Rsh values ................................................................................................................ 13

Notes ................................................................................................................................................. 14

3. Application ....................................................................................................................................... 15

To emulate an I/O driver circuit of logic IC ................................................................................. 15

To emulate a solar cell ................................................................................................................... 19

Page 4

1. Introduction

Ideal voltage source has zero-Ω output impedance and ideal current source has infinite

output impedance. Generally, such ideal source is suitable for a device/module

characterization. However in the real application environments, you cannot anticipate such

ideal condition. You may be surprised by seeing your device/module behave strangely. And

in a bad situation, you may stop working due to the voltage drop across the intolerable residual

resistance, wire, output resistance of power supply, and so on.

The voltage drop can be given by a function of the current which varies according to the load

resistance. So you can observe the affect of the voltage drop by emulating the voltage which

will be actually applied to the load. Then, you have to calculate and adjust the voltage (V to satisfy V



: residual resistance).



=V−I



×R



(V: output voltage at open, I

: load current,



Instead of above tasks, you may connect a real resistor to the instrument terminal externally.

Then you have to prepare variety of resistors and replace the resistor manually to observe its

dependency and change the resistance.

To avoid these troublesome tasks, you can use the Agilent B2961A/B2962A which provides

the programmable output resistance function. The B2961A/B2962A supports two operation

modes, constant and VI emulation, for this function. The constant mode lets the

B2961A/B2962A channel work as a voltage source with built-in constant series resistor (Rs) or

a current source with a built-in constant shunt resistor (Rsh). And the VI emulation mode lets

the channel work as a voltage source or current source with a built-in resistor which has a

non-linear I-V characteristics. By using this function, DC I-V characteristics of device/module

such as a battery can be emulated easily and effectively.

This document introduces the VI emulation mode of the programmable output resistance

function and the application examples by using the B2961A/B2962A. For the constant mode,

see another document “Using Constant Mode”, publication number B2960-90041.

)

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2. VI Emulation Mode

The VI emulation mode lets the B2961A/B2962A channel work as a source with a built-in

non-linear resistor. The channel can emulate an electronic devices or circuits which have a

non-linear four quadrant I-V characteristics. The characteristics is emulated by using the

impedance Z(I) which is a function of current and the admittance Y(V) which is a function of

voltage.

Simplified I-V characteristics of a battery cell is shown in Figure 1. When you draw a

tangent line at an operating point P in Figure 1 (a), its slope (ΔV/ΔI) is the impedance Z of

the device at the point P(Vp, Ip).

∆V

() =

∆I





And its reciprocal is the admittance Y.

∆I



() =

∆V



As shown above, Z and Y are the function of V or I. Using this fact, the I-V characteristics

is transformed into the Z-I (impedance-current) plane as shown in Figure 1 (b). Thus, the I-V

characteristics can be expressed by using the Z-I, V-Y, or their combination. For very high impedance, conductance (Y) can be used. In this case, zero impedance (Z=0, Y=∞) gives the

constant voltage, and zero admittance (Y=0, Z=∞) gives the constant current.

(a)

Figure 1 I-V characteristics of a battery cell and its transformation function into Z-I plane

(b)

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Emulation table and PWL interpolation

The B2961A/B2962A uses a user defined emulation table and the piecewise linear (PWL)

interpolation to express a non-linear DC I-V characteristics. The emulation table is considered

as a data list which can store up to 16 pairs of voltage and current data. The PWL

interpolation is a widely used technique in engineering for approximating a complex function by

a simple (linear) function.

A pair of voltage and current data makes a point on the I-V plane as shown in Figure 2.

And the B2961A/B2962A channel performs the operation of the constant mode using the

resistance (Rs or Rsh) given by the slope between two adjacent points. Figure 3 shows an

example of I-V characteristics with six I-V data.

Figure 2 Emulation table data and slope

Figure 3 Example of I-V characteristics

Agilent B2961A/B2962A setting parameters:

 Primary source mode (set to B2961A/B2962A front panel Mode): voltage (V) or current (I)  V and I source values (set to Output R (Emulation), emulation table)  V/I mode for transition between adjacent source values (set to Output R (Emulation),

emulation table)

Primary source mode and shape of I-V characteristics

Simplified block diagram of the B2961A/B2962A channel in the VI emulation mode is

shown in Figure 4. The upper part of the figure represents a voltage source with series

resistance (Rs) and the lower part represents a current source with shunt resistance (Rsh).

The channel initially works as a voltage source or a current source depending on the Mode

setting. This source mode is called as the primary source mode in this document. The

source mode for each transition between two adjacent points can be dynamically switched

according to the V/I mode set to the emulation table. By this mechanism, various shapes of

I-V characteristics can be emulated stably.

Page 7

Figure 4 Simplified block diagram, VI emulation mode

(a) Primary source mode: Voltage (b) Primary source mode: Current

Figure 5 I-V shapes allowed in VI emulation mode

The shape of I-V characteristics to emulate must be classified into one of the patterns

shown in Figure 5. For example, a battery emulation described above is classified into the

pattern shown in the quadrant-1 of (a). And to emulate a lamp, the quadrant-4 of (a) should

be used. In this case, V is the B2961A/B2962A channel output voltage and I is the output

current. Positive current flows to load from channel.

Page 8

Note that the primary source mode must be specified before the programmable output

resistance function is enabled. Also, the primary source mode must be voltage for the I-V

characteristics like the quadrant-1 or 3.

V/I mode setting

The emulation table is used to set the voltage and current values for each point on the DC

I-V characteristics as described above. Also the table contains the V/I mode for each

transition between two adjacent points which is a necessary parameter to select the

B2961A/B2962A channel operation, voltage source or current source, most suitable for each

point and transition.

An example of I-V characteristics is shown in Figure 6. Theoretically, this characteristics

can be emulated by using either a 5 V voltage source with 1 kΩ series resistor or a 5 mA

current source with 1 kΩ shunt resistor as shown in Figure 7. However, it is difficult to

emulate the characteristics by using either of them due to the affect of the load resistance.

Generally, the voltage source is effective for R

 Rsh.

Load

Figure 6 Linear I-V characteristics of Vopen=5 V

and Ishort=5 mA



Rs and the current source is effective for

Load

Figure 7 Two equivalent circuits to realize

characteristics shown in Figure 6

Page 9

Figure 8 and Figure 9 show the load voltage measurement results of the above circuit (Figure

7) with several load resistors. The voltage source (V mode) works fine for R

output oscillates for R

for R

 1 kΩ and its output starts oscillating over 2 kΩ. In this case, the critical load

Load

= 100 Ω. On the other hand, the current source (I mode) works fine

Load



1 kΩ, and its

Load

resistance value is 1 kΩ that is equal to Rs and Rsh. So the V/I mode should be switched at

this point which is actually not a point but a band with some width.

= 10 MΩ > Rs

Load

Stable

Figure 8 V mode operation with various R

= 2 kΩ > Rs

Load

Stable

= 1 kΩ = Rs

Load

Stable

Load

= 100 Ω < Rs

Load

Unstable

= 10 MΩ > Rsh

Load

= 2 kΩ > Rsh

Load

Unstable

Figure 9 I mode operation with various R

becoming Unstable

= 1 kΩ = Rsh

Load

Stable

Load

= 0.1 Ω < Rsh

Load

Stable

Page 10

Emulation table setting example

The I-V characteristics of a typical solar cell is shown in Figure 10. Dotted lines represent

load lines for several resistances. In this example, the I-V characteristics is split into 5 slopes,

S1 to S5. And the output resistance (S3) becomes the same as the load resistance at the

operating point P3. So the emulation table should be defined as shown in Table 1.

)

(

Figure 10 I-V characteristics of typical solar cell

Table 1 Voltage, Current, and V/I mode settings for above characteristics

Operating

point

Voltage Current Slope

Output

impedance

V/I mode

P1 (short) V1=0 I1

P2 V

P3 V

P4 V

P5 V

P6 (open) V6 I

−



I−I

−



I−I

−



I−I

−



I−I

−



I−I











Note that the system requires the descending order (from large value to small value) for the

Current column in the table.

This example assumes that the load capacitance is negligible and there is no internal bias

source in the load. If any bias source exists in the load, the load resistance looks different

and the V/I mode may need to be changed.

Page 11

Combination of V/I mode

If the primary source mode is voltage

Combination of the V/I mode must be one of the following conditions (Figure 11).

(1) V mode only

(2) I mode (I > 0) to V mode

(3) V mode to I mode (I < 0)

(4) I mode (I > 0) to V mode to I mode (I < 0)

The I-V curve must be started by the positive current and ended by the negative current.

The I mode cannot be used within ±1 % of full scale of the current range (or ±10 % for the

10 nA range). So, the V mode must be used for this ±1 % region (or ±10 % region for the 10

nA range).

(1) V only

(3) V-I (4) I-V-I

Figure 11 V/I mode when the primary source mode is voltage

(2) I-V

Page 12

If the primary source mode is current

Combination of the V/I mode must be one of the following conditions (Figure 12).

(1) I mode only

(2) V mode (V < 0) to I mode

(3) I mode to V mode (V > 0)

(4) V mode (V < 0) to I mode to V mode (V > 0)

The I-V curve must be started by the negative voltage and ended by the positive voltage.

The V mode cannot be used within ±1 % of full scale of the voltage range (or ±10 % for the

200 mV range). So, the I mode must be used for this ±1 % region (or ±10 % region for the 200

mV range).

Start

I mode

(1) I only

End

(2) V-I

(3) I-V (4) V-I-V

Figure 12 V/I-mode when the primary source mode is current

Page 13

Bad examples

Bad examples of V/I mode combination are shown in Figure 13.

(a) is a bad example for the combination shown in Figure 11 (3). The positive current is not

allowed for the I mode, also the negative resistance (Rs or Rsh) is not allowed.

(b) is a bad example for the combination shown in Figure 12 (3). The V mode cannot be

used within ±1 % of full scale of the voltage range (or ±10 % for the 200 mV range).

(a)

Figure 13 Bad examples of V/I mode combination

(b)

Available Rs/Rsh values

See the document “Using Constant Mode”, publication number B2960-90041. The available

Rs/Rsh values for the constant mode are also effective for the VI emulation mode. However,

the negative resistance/conductance is not allowed for the VI emulation mode. So, the I-V

characteristics always shows the curve from upper left to lower right as shown in Figure 11

and Figure 12. Also, the shape of I-V characteristics is limited due to the internal

configuration as described above.

Page 14

Notes

 The channel can be used for the

the load voltage or current.

 The channel can be used betwee

emulation table. Do not apply v

 The channel automatically selec

emulation table setting. They a

current values. Those ranges a

 The channel output stability can

filter. However, this increases

 Do not connect the other B2961

which uses the programmable o

 When the channel works as a vo

undesirable noise increases. T

reduced by increasing the time c

 For the setting error of Rs/Rsh,

number B2960-90041.

 If you confirm the emulation res

DC emulation. It cannot respond to the fast tran

n the minimum value and the maximum value set

oltage/current outside this range to the channel.

s the voltage and current ranges according to the

re the smallest range that covers all voltage value

e fixed during source output.

be improved by increasing the time constant of th

he response time.

/B2962A channel in series or parallel to the chan

tput resistance function.

ltage source with high Rs and high current range,

is fundamental noise cannot be eliminated but ca

nstant of the output filter because it cuts off the

ee the document “Using Constant Mode”, publica

lt, use voltage source and current meter (VSIM) f

ition of

o the

or all

output

oise.

ion

r the

high impedance area (I mode) of

(ISVM) for the low impedance ar

for each measurement. Otherw

For example, as shown in the VS

monitored correctly by VSIM. S

correctly by ISVM.

the VI emulation and use current source and volt

a (V mode). Most suitable instrument should b

ise, the emulation result cannot be monitored corr

M line of Figure 14, the low impedance area cann

imilarly, the high impedance area cannot be monit

eter

used

ectly.

t be

red

Figure 14 VI emulation result measured

by external instruments

Page 15

3. Application

Agilent B2961A/B2962A Power Source can be a voltage source or a current source which

enables wide range voltage/current output and advanced test and evaluation. And its

programmable output resistance function is effective for several applications such as error

compensation, source emulation, resistance emulation, and so on. This section introduces

the following examples for using this function.

 To emulate an I/O driver circuit of logic IC  To emulate a solar cell

To emulate an I/O driver circuit of logic IC

Introduction

I-V characteristics (IOH: Logic-High level output current, IOL: Logic-Low level input current) of

a logic IC driver circuit are shown in Figure 15. They are typical characteristics which you can

obtain from an IC data sheet or an IBIS (Input/Output Buffer Information Specification) model

file if available. As shown in the graph, the output resistance of the driver circuit is not linear.

And the characteristics are affected by the operating conditions such as applied voltage,

temperature, and so on.

For designing a device, a module, or a circuit which receives the driver output, it is important

to check its operation with several variations of driver outputs. However it is difficult and

inefficient to prepare several driver circuits or to realize several operating conditions. Then,

the VI emulation by using the B2961A/B2962A is an effective solution to obtain the various

outputs easily.

(a) I

(b) IOL

Figure 15 I-V characteristics of a driver circuit (IOH and IOL) for various power supply (VCCIO)

Page 16

Figure 16 Current flow between I/O driver and load

Emulation example

The following example is for the IOH emulation of 3.3 volts VCCIO. The settings of the

B2961A/B2962A are shown below. For this emulation, the primary source mode must be

voltage because the shape is similar to the pattern of the quadrant-1 shown in Figure 5 (a).

 Primary source mode (B2961A/B2962A front panel Mode setting): voltage (V)  V and I source values (in emulation table): See Voltage and Current columns in Figure 17.  V/I mode (in emulation table): See Mode column in Figure 17.

Figure 17 shows the setup image when the VI Emulation Sample Program is used. The

program is available from Agilent B2900 web site (http://www.agilent.com/find/b2900a).

This program automatically calculates the output resistance and conductance, and displays the

I-V characteristics.

B2961A/B 2962A VI Emulat ion Sample Program, R ev. 1.2, 2012/9/25

ADDRESS

TIMEOUT

*IDN?

Primary Voltage(0)

Voltage

Index

0 0 62 I 500 0.002 1 0.5 61 I 250 0.004 2 1 59 I 166.6666667 0.006 3 1.5 56 I 83.33333333 0.012 4 2 50 V 35.71428571 0.028 5 2.5 36 V 25 0.04 6 3 16 V 12.5 0.08

73.20 V 10 0.1

83.3-10

9 10 11 12 13 14 15

Current

[V]

[mA]

UsbInstrument1

Mode

V(0), I(1)

3000

*IDN?

Output resistance

(slope) [V/I]

Output conductance (1/slope) [I/V]

Disable

Connect

V-I characteristics

CUrrent [mA]

0 0 .5 1 1.5 2 2 .5 3 3.5

-10

-20

Voltage [V]

Figure 17 B2961A/B2962A VI Emulation Sample Program settings for IOH emulation

Page 17

Figure 18 Load line for selecting V/I mode

The V and I source values can be selected by reading the values on the curve shown in

Figure 18. This example assumes that the load does not have internal bias and the load line

starts from the origin.

The V/I mode should be selected after finding the point which satisfies R

According to Figure 18, this point is on the 46 Ω load line. So, I mode should be used for R



46 Ω, and V mode should be used for R



46 Ω. Depending on the emulation result, you

Load

= Rs = Rsh.

Load

may need to adjust the setting.

Figure 19 shows the emulation result. The result can be monitored by using an external

instrument. Then use voltage source and current meter (VSIM) for the high impedance area (I

mode) of the VI emulation, and use current source and volt meter (ISVM) for the low

impedance area (V mode).

0.07

0.06

0.05

0.04

0.03

Cu rrent [A]

0.02

0.01

00.511.522.533.5

Voltage [V]

Figure 19 IOH characteristics emulation result measured by external instruments

Page 18

The following example is for the IOL emulation of the same device. For this emulation, the

primary source mode must be voltage because the shape is similar to the pattern of the

quadrant-4 shown in Figure 5 (a).

 Primary source mode (B2961A/B2962A front panel Mode setting): voltage (V)  V and I source values (in emulation table): See Voltage and Current columns in Figure 20.  V/I mode (in emulation table): See Mode column in Figure 20.

B2961A/B 2962A VI Emulat ion Sample Program, R ev. 1.2, 2012/9/25

ADDRESS

TIMEOUT

*IDN?

Primary Voltage(0)

UsbInstrument1

3000

*IDN?

Connect

Voltage

Index

0 0 0 V 16.66666667 0.06 1 0.5 -30 V 29.41176471 0.034 2 1 -47 V 83.33333333 0.012 3 1.5 -53 I 500 0.002 4 2 -54 I 500 0.002

52.5-55I inf 0 63-55I inf 0

73.2-55I inf 0 84-55

9 10 11 12 13 14 15

Current

[V]

[mA]

Mode

V(0), I(1)

Output resistance

(slope) [V/I]

Output conductance (1/slope) [I/V]

Disable

V-I characteristics

012345

-10

-20

-30

CUrrent [mA]

-40

-50

-60

Voltage [V]

Figure 20 B2961A/B2962A VI Emulation Sample Program settings for IOL emulation

012345

-0.01

-0.02

-0.03

Current [A]

-0.04

-0.05

-0.06 Vo ltage [V]

Figure 21 IOL characteristics emulation result measured by external instruments

As described above, two characteristics of a logic IC driver circuit are emulated easily by

using the B2961A/B2962A. Special setup for the VI emulation is the emulation table only.

Just by filling the table with appropriate V and I values, the B2961A/B2962A can emulate

various DC output characteristics.

Page 19

To emulate a solar cell

Introduction

Solar cell is attractive device as it is a sustainable energy source, and has been used for

wide applications, for example, portable devices or remote sensing units, and such. Output

I-V characteristics of solar cell is affected by the operating conditions such as light power,

temperature, and so on. Aging and the stain on the surface also affect the performance.

For designing a device, a module, or a circuit which uses solar cell as power source, it is

important to check its operation in several operating conditions. However it is difficult and

inefficient to use actual solar cell or to realize several operating conditions. Then, the VI

emulation is an effective solution to obtain the various power conditions easily.

Emulation example

Simplified equivalent circuit of solar cell is shown in Figure 22. It consists of the ideal

current source, a diode, a shunt resistor (Rsh), and a series resistor (Rs) which contains

internal series resistor and external wire resistance. Generally, Rsh causes leakage current,

and Rs causes voltage drop depending on load current.

Figure 22 Simplified equivalent circuit of

solar cell

Figure 23 I-V characteristics of solar cell to emulate

Figure 23 shows I-V characteristics of a solar cell. This output characteristics can be

emulated by the following setup.

 Primary source mode (B2961A/B2962A front panel Mode setting): voltage (V)  V and I source values (in emulation table): See Voltage and Current columns in Figure 24.  V/I mode (in emulation table): See Mode column in Figure 24.

Page 20

The primary source mode must be voltage because the shape is similar to the pattern of the

quadrant-1 shown in Figure 5 (a).

The V and I source values can be selected by reading the curve shown in Figure 23. The

values can be also selected from calculation or simulation like SPICE for emulating the output

characteristics in the several temperature conditions, various darkness conditions, and such.

The V/I mode should be selected after finding the point which satisfies R

= Rs = Rsh.

Load

According to Figure 23, this point is on the 6.5 Ω load line. So, I mode should be used for R



6.5 Ω, and V mode should be used for R



6.5 Ω. Emulation result is shown in Figure 25.

Load

Depending on the emulation result, you may need to adjust the setting.

B2961A/B 2962A VI Emulat ion Sample Program, R ev. 1.2, 2012/9/25

ADDRESS

TIMEOUT

*IDN?

Primary Voltage(0)

Voltage

Index

00130I 100 0.01 1 0.2 128 I 66.66666667 0.015 2 0.4 125 I 50 0.02 3 0.6 121 I 16.66666667 0.06 4 0.7 115 I 6.666666667 0.15 5 0.8 100 V 2.5 0.4 6 0.85 80 V 0.75 1.333333333 7 0.88 40 V 0.4 2.5

80.9-10

9 10 11 12 13 14 15

Current

[V]

[mA]

UsbInstrument1

Mode

V(0), I(1)

3000

*IDN?

Output resistance

(slope) [V/I]

Output conductance (1/slope) [I/V]

Connect

V-I characteristics

140

120

100

CUrrent [mA]

0 0.2 0.4 0.6 0.8 1

-20

Voltage [V]

Load

Disable

Figure 24 B2961A/B2962A VI Emulation Sample Program settings for solar cell

0.14

0.12

0.1

0.08

Current

0.06

0.04

0.02

0 0.10.20.30.40.50.60.70.80.9 1

Voltage

Figure 25 Solar cell I-V characteristics emulation result measured by external instruments