Datasheet CN-0200 Datasheet (ANALOG DEVICES)

Circuit Note

Circuits from the Lab™ circuits from Analog Devices have been designed and built by Analog Devices

each circuit, and their function and performance have been tested and verified in a lab environment at
room temperature. However, you are solely responsible for testing the circuit and determining its
suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices
be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause

+

+

+

+

+

968 3 2

15 17 16 19

20

24

1

CLR

IOV

CCVCCVDD

BUFFERED

V

REFP

V

REFP

V

SS

V

REFN

AGND

–10V TO +10V

OUTPUT

VOLTAGE

0V TO +10V

DGND

V

OUT

R

FB

7

LDAC

11

SDO

14

INV

13

SCLK

SYNC

AD5780

AD8675

AD8675

12

SDIN

4

RESET

+15V

+15V

+10V

–15V

–15V

10µF

C1
10µF

A1

A2

0.1µF

10µF

+3.3V +15V

+15V

–15V

0.1µF

10µF

0.1µF

10µF

0.1µF

0.1µF

R1

1.5kΩ

R3*

1kΩ

6.8kΩ

6.8kΩ

SPI INTERFACE

AND DIGITAL

COTNROL

R2*

1kΩ

ADR445

GND

V

INVOUT

09697-001

*FOR OPTIMUM PERFORMANCE OVER TEMPERATURE,
R2 AND R3 SHOULD BE IN A SINGLE PACKAGE.

Circuits from the Lab™ reference circuits are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges. For more
information and/or support, visit www.analog.com/CN0200.

18-Bit, Linear, Low Noise, Precision Bipolar ±10 V DC Voltage Source

EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Boards

AD5780 Circuit Evaluation Board (EVAL-AD5780SDZ)
System Demonstration Platform (EVAL-SDP-CB1Z)

Design and Integration Files
Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTION AND BENEFITS

The circuit shown in Figure 1 is an 18-bit linear, low noise,
precision bipolar (±10 V) voltage source with a minimum

CN-0200

Devices Connected/Referenced

AD5780 True 18-Bit, Voltage Output DAC

AD8675

AD8676

ADR445

amount of external components. The AD5780 DAC is an 18-bit,
unbuffered voltage output DAC operating from a bipolar supply
of up to 33 V. The AD5780 accepts a positive reference input
range of 5 V to VDD − 2.5 V, and a negative reference input
range of VSS + 2.5 V to 0 V. Both reference inputs are buffered
on the chip, and external buffers are not required. The AD5780
offers a relative accuracy specification of ±1 LSB maximum, and
operation is guaranteed monotonic, with a ±1 LSB maximum
DNL specification.

Ultraprecision, 36 V, 2.8 nV√Hz,
Rail-to-Rail Output Op Amp

Ultraprecision, 36 V, 2.8 nV√Hz, Dual
Rail-to-Rail Output Op Amp

Ultralow Noise 5V LDO XFET® Voltage
Reference

Rev.0

engineers. Standard engineering practices have been employed in the design and construction of

whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page)

Figure 1. 18-Bit Accurate, +10 V Voltage Source (Simplified Schematic: All Connections and Decoupling Not Shown)

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
Fax: [phone] ©2011 Analog Devices, Inc. All rights reserved.

www.analog.com

CN-0200 Circuit Note

–0.4

–0.3

–0.2

–0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50000 100000 150000 200000 250000

INL (LSB)

DAC CODE

09697-002

–0.2

–0.1

0

0.1

0.2

0.3

0.4

0.5

0 50000 100000 150000 200000 250000

DNL (LSB)

DAC CODE

09697-003

The AD8675 precision op amp has low offset voltage (75 µV
maximum), low noise (2.8 nV/√Hz typical), and is an optimum
output buffer for the AD5780. The AD5780 has two internal
matched feedforward and feedback resistors, which are
connected to the AD8675 op amp and provide the 10 V offset
voltage. This allows an output voltage swing of ±10 V with a
single external 10 V reference.

The digital input to the circuit is serial and is compatible with
standard SPI, QSPI, MICROWIRE®, and DSP interface standards.
For high accuracy applications, the compact circuit offers high
precision, as well as low noise—this is ensured by the
combination of the AD5780, ADR445, and AD8675 precision
components.

This combination of parts provides industry-leading 18-bit
integral nonlinearity (INL) of ±1 LSB and differential
nonlinearity (DNL) of ±0.75 LSB, with guaranteed
monotonicity, as well as low power, small PCB area, and
cost effectiveness in an LFCSP package.

CIRCUIT DESCRIPTION

The digital-to-analog converter (DAC) shown in Figure 1 is the

AD5780, a high voltage, 18-bit converter with SPI interface,

offering ±1 LSB INL, ±0.75 LSB DNL, and 7.5 nV/√Hz noise
spectral density. The AD5780 also exhibits an extremely low
temperature drift of 0.005 LSB/°C.

Figure 1 shows the AD5780 configured in a gain-of-two mode
such that a single reference source can be used to generate a
symmetrical bipolar output voltage range. This mode of
operation uses an external op amp (A2), as well as on-chip
resistors (see AD5780 data sheet), to provide the gain of 2.
These internal resistors are thermally matched to each other
and to the DAC ladder resistance, resulting in ratiometric
thermal tracking. The output buffer is again the AD8675, used
for its low noise and low drift. This amplifier is also used (A1)
to amplify the +5 V reference voltage from the low noise

ADR445 to +10 V. R2 and R3 in this gain circuit are precision

metal foil resistors with 0.01% tolerance and a temperature
coefficient resistance of 0.6 ppm/°C. For optimum performance
over temperature, R1 and R2 should be in a single package, such
as the Vishay 300144 or VSR144 series. R2 and R3 are selected
to be 1 kΩ to keep noise in the system low. R1 and C1 form a
low-pass filter with a cutoff frequency of approximately 10 Hz.
The purpose of this filter is to attenuate voltage reference noise.

Linearity Measurements

The precision performance of the circuit shown in Figure 1 is
demonstrated on the EVAL -AD5780SDZ evaluation board
using an Agilent 3458A Multimeter. Figure 2 shows the integral
nonlinearity as a function of DAC code is within specifications
of ±1 LSB.

Figure 2. Integral Nonlinearity vs. DAC Code

Figure 3 shows that the differential nonlinearity as a function of
DAC code is within the −0.25 LSB to +0.75 LSB specification.

Figure 3. Differential Nonlinearity vs. DAC Code

Noise Drift Measurements

To be able to realize high precision, the peak-to-peak noise at
the circuit output must be maintained below 1 LSB, which is

76.29 µV for 18-bit resolution and a 20 V peak-to-peak voltage
range.

A real-time noise application will not have a high-pass cutoff at

0.1 Hz to attenuate 1/f noise but will include frequencies down
to dc in its pass band. With this in mind, the measured peak-to­peak noise is realistically shown in Figure 4. In this case, the
noise at the output of the circuit was measured over a period of
100 seconds, effectively including frequencies as low as 0.01 Hz
in the measurement. The upper frequency cutoff is at approxi­mately 14 Hz and is limited by the measurement setup.

Rev. 0 | Page 2 of 6

Circuit Note CN-0200

–40

–30

–20

–10

0

10

30

20

40

0 20 40 60 80 100

NOISE (µV)

TIME (Seconds)

09697-004

V

DD

= +15V

V

SS

= –15V

V

REFP

= +10V

V

REFN

= 0V

ZERO SCALE

HALF SCALE

FULL SCALE

–3

–2

–1

0

1

3

2

4

0 20 40 60 80 100

NOISE (µV)

TIME (Seconds)

09697-005

VDD = +15V
V

SS

= –15V

V

REFP

= +10V

V

REFN

= 0V

HALF SCALE

FULL SCALE

ZERO SCALE

Figure 4 shows the peak-to-peak values are 1.2 µV for zero-scale

output, 32 µV for half-scale output, and 64 µV for full-scale
output.

The zero-scale output voltage exhibits the lowest noise because
it represents the noise from the DAC core only. The noise
contribution from each voltage reference path is attenuated by
the DAC when the zero-scale code is selected.

Figure 4. DAC Output Voltage Noise Measured Over 100 Second Period for

As the time period over which the measurement is taken is
increased, lower frequencies will be included, and the peak-to­peak value will increase. At low frequencies, temperature drift
and thermocouple effects become contributors to noise. These
effects can be minimized by choosing components with low
thermal coefficients. In this circuit, the main contributor to low
frequency 1/f noise is the voltage reference. It also exhibits the
greatest temperature coefficient value in the circuit of 3 ppm/°C.
A temperature controlled ultralow noise reference would be
required to improve the half-scale and full-scale DAC output
noise.

Figure 5 shows the performance of the signal chain by replacing
the ADR445 with a Krohn Hite Model 523 Precision Reference
set for +5 V.

Complete schematics and layout of the printed circuit board
can be found in the CN-0200 Design Support Package:

www.analog.com/CN0200-DesignSupport .

Full Scale (Red), Half Scale (Green), and Zero Scale (Blue)

Figure 5. DAC Output Voltage Noise Measured Over 100 Second Period for

Full Scale (Red), Half Scale (Green), and Zero Scale (Blue) with Precision

Reference Source

COMMON VARIATIONS

The AD5780 will support a wide variety of output ranges from
0 V to +5 V up to ±10 V, and values in between. The gain-of-2
configuration, as shown in Figure 1, can be used if a
symmetrical output range is required. This mode is selected by
setting the RBUF bit of the AD5780 internal control register to
a Logic 0. If an asymmetrical range is required, individual
references can be applied at VREFP and VREFN, and the output
buffer should be configured for unity gain as described in the

AD5780 data sheet. This is done by setting the RBUF bit of the
AD5780 internal control register to a Logic 1.

The AD8676 is a dual version of the AD8675 op amp and can be
used in the circuit if desired.

CIRCUIT EVALUATION AND TEST

Equipment Required

• System Demonstration Platform (EVA L-SDP-CB1Z)

• E VAL -AD5780SDZ Evaluation Board and Software

• Agilent 3458A multimeter

• PC (Windows 32-bit or 64-bit)

• National Instruments GPIB to USB-B interface cable

• SMB cable (1)

Software Installation

The AD5780 evaluation kit includes self-installing software on
a CD. The software is compatible with Windows XP (SP2) and
Vista (32-bit and 64-bit). If the setup file does not run
automatically, you can run the setup.exe file from the CD.

Rev. 0 | Page 3 of 6

CN-0200 Circuit Note

09697-006

Install the evaluation software before connecting the evaluation
board and SDP board to the USB port of the PC to ensure that
the evaluation system is correctly recognized when connected to
the PC.

1. After installation from the CD is complete, power up
the AD5780 evaluation board as described in the
Power Supplies section of UG-256. Connect the SDP
board (via either Connector A or Connector B) to the

AD5780 evaluation board and then to the USB port of

your PC using the supplied cable.

2. When the evaluation system is detected, proceed
through any dialog boxes that appear. This completes
the installation.

Functional Diagram

A functional diagram of the test setup is shown in Figure 7.

Power Supply Configuration

The following supplies must be provided:

• 3.3 V between the VCC and DGND on Connector J1
for the digital supply of the AD5780. Alternatively,
place Link 1 in Position A to power the digital
circuitry from the USB port via the SDP board
(default setting).

• +12 V to +16.5 V between the VDD and AGND inputs
of J2 for the positive analog supply of the AD5780.

• −12 V to −16.5 V between the VSS and AGND inputs
of J2 for the negative analog supply of the AD5780.

Figure 6. Evaluation Software Main Window

Rev. 0 | Page 4 of 6

J2-3

+VDD

−15V

AGND

DUAL POWER SUPPLY

SDP

CON A
OR
CON B

120-PIN SDP

USB

PC

AGILENT

3458A MULTIMETER

GPIB

USB

USB

SMB

EVAL-AD5780SDZ

VOUT_BUF

−VSS

J2-2 J2-1

+15V

J4

COM

09697-007

Circuit Note CN-0200

Figure 7. Functional Block Diagram of Test Setup

Link Configuration Setup

The default link options are listed in Table 1. By default, the
board is configured with VREFP = +10 V and VREFN = −10 V
for a ±10 V output range.

Table 1. Default Link Options

Link No. Option

LK1 A
LK2 B
LK3 A
LK4 Removed
LK5 Removed
LK6 Removed
LK7 Removed
LK8 C
LK9 Inserted
LK11 Inserted

To configure the board for the circuit shown in Figure 1,
the following changes must be made to the default link
configuration in Table 1:

1. Place LK3 in position B.

2. Insert LK4.

3. Place LK8 in position B.

These changes configure the output buffer amplifier for a gain
of 2 and connect the VREFN pin of the AD5780 to ground.

Please refer to User Guide UG-256 for more information on the

EVA L-AD5780SDZ test setup.

Rev. 0 | Page 5 of 6

Test

The VOUT_BUF SMB connector is connected to the Agilent
3458A multimeter. The linearity measurements are run using
the Measure DAC Output Tab on the AD5780 GUI.

The noise drift measurement is measured on the VOUT_BUF
SMB connector also. The output voltage is set using the Prgram
Voltage tab in the AD5780 GUI. The peak-to-peak noise drift is
measured over 100 seconds.

For more details on the definitions and how to calculate the
INL, DNL, and noise from the measured data, see the
"TERMINOLOGY" section of the AD5780 data sheet and also
the following reference: Data Conversion Handbook, "Testing

Data Converters," Chapter 5, Analog Devices.

LEARN MORE

CN-0200 Design Support Package:

www.analog.com/CN0200-DesignSupport

Egan, Maurice. "The 20-Bit DAC Is the Easiest Part of a 1-ppm-

Accurate Precision Voltage Source," Analog Dialogue, Vol.
44, April 2010.

Kester, Walt. 2005. The Data Conversion Handbook. Analog

Devices. Chapters 3, 5, and 7.

MT-015 Tutorial, Basic DAC Architectures II: Binary DACs.

Analog Devices.

MT-016 Tutorial, Basic DAC Architectures III: Segmented DACs.

Analog Devices.

CN-0200 Circuit Note

MT-031 Tutorial, Grounding Data Converters and Solving the

Mystery of AGND and DGND. Analog Devices.

MT-035 Tutorial, Op Amp Inputs, Outputs, Single-Supply, and

Rail-to-Rail Issues. Analog Devices.

MT-101 Tutorial, Decoupling Techniques. Analog Devices.
Voltage Reference Wizard Design Tool.
CN-0177 Circuit Note, 18-Bit, Linear, Low Noise, Precision

Bipolar ±10 V DC Voltage Source.
CN-0191 Circuit Note, 20-Bit, Linear, Low Noise, Precision,

Bipolar ±10 V DC Voltage Source.
User Guide UG-256 for EVA L-AD5780SDZ.

Data Sheets and Evaluation Boards

AD5780 Data Sheet and Evaluation Board
AD8676 Data Sheet
ADR445 Data Sheet

REVISION HISTORY

11/11—Revision 0: Initial Version

(Continued from first page) Circuits from the La b circuits are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you
may use the Circuits from the Lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by
application or use of the Circuits from the Lab circuits. Information furnished by Analog Devices is believed to be accurate and reliable. However, "Circuits from the Lab" are supplied "as is"
and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular
purpose an d no responsibil ity is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices
reserves the right to change any Circuits from the Lab circuits at any time without notice but is under no obligation to do so.

©2011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
CN09697-0-11/11(0)

Rev. 0 | Page 6 of 6