User Guide for the AD7944/AD7985/AD7986

14-/16-/18-Bit PulSAR ADCs

Features

• Full-featured evaluation board for the AD7944/AD7985/AD7986

• PC control with EVAL-CED1Z converter board

• Software for time and frequency domain analysis

• Versatile analog signal conditioning circuitry

• On-board reference, clock oscillator, and buffers

• Standalone capability

Figure 1 EVAL-AD7944/AD7985/AD7986 evaluation board

System Requirements:

• Windows XP SP2, Vista, or Windows 7

• USB 2.0 port

Software Needed:

• Enclosed CD or website download

Evaluation Kit Contents:

• Evaluation board (EVAL-AD7944EDZ, EVAL-AD7985EDZ, or EVAL-AD7986EDZ)

• Software CD

Documents Required:

• AD7944, AD7985, AD7986 data sheets

Equipment Required:

• Precision DC and AC signal sources

• Band-pass filter (16-/18-bit rated)

• SMB cable

• EVAL-CED1Z board

• 7V DC supply adapter

General Description

The EVAL-AD79XXEDZ evaluation board targets 20-lead PulSAR ADCs. On-board components include a high precision, buffered band gap 5.0V reference (ADR435), reference buffers (AD8032), a signal conditioning circuit with two op-amps (AD8021), and an FPGA for deserializing the serial conversion results. This evaluation board interfaces to the EVAL-CED1Z capture board via a 96-pin DIN connector. SMB connectors are provided for the low-noise analog signal source.

Figure 2 EVAL-AD7944/AD7985/AD7986 evaluation board block diagram

The AD7944 is a 14-bit, 2.5 MSPS SAR ADC, the AD7985 is a 16-bit, 2.5 MSPS SAR ADC, and the AD7986 is an 18-bit, 2.0 MSPS SAR ADC. Each device features an internal conversion clock, an internal reference (and buffer), error correction circuits, and a versatile serial interface port.

Quickstart

1. Install the software from the CD or website download. Disconnect the evaluation board during installation.

2. Connect the EVAL-CED1Z to the evaluation board.

3. Connect the 7V power supply adapter to the EVAL-CED1Z connector J4.

4. Connect the EVAL-CED1Z via USB to the PC (drivers auto-detect).

5. Launch the evaluation software from the Programs menu.

6. Select the device from the dropdown (AD7944, AD7985, or AD7986).

7. Apply the signal source to the AIN+/AIN- SMB inputs.

8. Configure the signal source appropriately.

9. Initiate single capture (F3) or continuous capture (F4).

10. Configure the software per the Software Operation section.

Note

The measurements made by Analog Devices use the Audio Precision SYS-2522.

Evaluation Board Hardware

Power Supplies

Each supply is decoupled where it enters the board and again at each device. A single ground plane is used on this board to minimize the effect of high frequency noise interference.

Standalone Operation

The evaluation board can operate without the EVAL-CED1Z controller. It requires ±5V, +12V, +7V, or +2.5V power supplies (see the design support package for detailed connection information).

Grounding

The evaluation board ground plane is separated into two sections: a plane for the digital interface circuitry and an analog plane for the analog input and external reference circuitry. These planes are connected directly beneath the ADC converter to minimize noise coupling.

Conversion Control

The on-board FPGA performs a number of digital functions, one of them being the deserialization of the serial conversion results as the EVAL-CED1Z data capture board uses a 16-bit parallel interface.

Analog Inputs

The analog inputs J1 and J2 are SMB (push-on) connectors, buffered with dedicated amplifier circuitry (A2, A3) and discrete components as shown in the schematic. The circuit allows for different configurations:

• Gain adjustment

• Input range scaling

• Filtering

• Addition of a DC component

• Use of different op-amps and supplies

The analog input amplifiers are set as unity-gain buffers at the factory, with supplies set for +7V to -5V ranges. Both A2 and A3 are set at midscale generated from a buffered reference voltage divider or internal ADC reference.

The AD7986 uses differential inputs; the AD7944 and AD7985 use a single-ended path.

For FFT testing, a very low distortion AC source is required. For low-frequency testing, an audio precision source can be used directly because the outputs on these are isolated.

Serial Interface

The 3-wire serial interface SDI, SCK, and SDO together with CNV are present on the digital interface test points, and FPGA-buffered versions are on the 96-pin connector, P1.

Jumpers, Solder Pads and Test Points

Table 1 3-Pin Jumper Descriptions

Jumper	Default Position	Function
P2	REF to middle	ADC REF/REFIN select
P9	REFS to VREF	On-board/external reference selection
P10	BUF to middle	Selection of Amplifier U2 or bypass
P11	REFIN to GND	Internal reference/buffer selection (with P12, P9)
P12	PDREF to VIO	Internal/external reference selection

Table 2 Solder Pad Descriptions

Solder Pad	Default Position	Function
JP1, JP2	A2, A3 (bottom to middle)	ADC inputs; top pad to middle bypasses A2/A3
JP3	ADC specific	Single/differential input selection
JP9, JP10	Left pads	10-lead/20-lead amplifier selection
VDRV-	-5 VA	Buffer amp negative supply: GND or -5 VA
VDRV+	+7V	Buffer amp positive supply: 12V, 7V, or 5V
VCC REF	+7V	Reference circuit supply: 12V or 7V
AVDD	+2.5V	ADC analog core supply: 2.5V or 5V (max 2.5V)
DVDD	+2.5V	ADC digital core supply: 2.5V or 5V (max 2.5V)
BVDD	+5V	ADC 5V supply: 5V on-board or externally
VIO	+2.5V	ADC digital I/O supply voltage

Reference Options

External Reference (Factory Configuration)

The board includes an ADR435 5V precision reference. The best attainable SNR is achieved by using the maximum reference voltage of 5V.

Table 3 Factory Reference Jumper Configuration

Jumper	Setting
P2	REF and middle
P9	REFS to VREF
P10	BUF to middle
P11	REFIN to GND
P12	PDREF to VIO
BVDD	5V (factory default)

Two external reference methods are available:

1. Unbuffered: Leave P10-P12 as factory settings, open P2, connect source to REF test point.

2. Buffered: Replace P2, open P9, apply source to VREF test point.

ADC Reference Supply, BVDD

The board includes a 5V source at solder pads (5V or EXT_B) and test point EXT_B. For the best performance, derive this supply from the external reference.

Internal 4.096V Reference

The ADC has an internal 4.096V precision reference and can be used on most applications. Connecting PDREF to GND enables the internal reference.

Table 4 Internal Reference Jumper Configuration

Jumper	Setting
P2	Open
P9	REFS to VREF
P10	Don’t care
P11	Open
P12	PDREF to GND
BVDD	5V (factory)

Internal Reference Buffer

The internal reference buffer is useful when using an external 1.2V reference. Applying 1.2V to REFIN produces 4.096V at the ADC REF pin.

Method 1: REFIN Test Point

Table 5 External Reference Buffer Configuration (REFIN Test Point)

Jumper	Setting
P2	Open
P9	Don’t care
P10	Don’t care
P11	Open
P12	PDREF to VIO
BVDD	5V (factory default)

Method 2: Divide Down

Uses U2 op-amp to divide 5V ADR435 output to 1.2V via R2/R4 = 1 kOhm/316 Ohm.

Table 6 External Reference Buffer Configuration (Divide Down)

Jumper	Setting
P2	REFIN to middle
P9	REFS to VREF
P10	BUF to middle
P11	REFIN to Pin 1
P12	PDREF to VIO
BVDD	5V (factory default)

Evaluation Board Software

Pre-Installation

Important

The EVAL-CED1Z board must not be connected to the USB port of the PC until after the software is installed. The green LED on the board confirms power; connecting the 7V DC supply is acceptable before installation.

Software Installation

Close all Windows applications before installation. The CD is included; latest versions are also available on analog.com. The user must accept the license agreement during the installation process.

1. Extract the software using WinZip (rather than running setup.exe directly).

2. Run setup.exe from the extracted folder.

3. Follow the on-screen instructions.

4. Remove prior versions via Control Panel > Add or Remove Programs if needed.

Figure 3 License agreement acceptance

Figure 4 Setup.exe initiation

Figure 5 Default installation directory selection

Figure 6 Software installation progress

Figure 7 Installation completion confirmation

USB Drivers

The USB drivers install separately after the main software installation. Click Install when the driver installation wizard appears.

Figure 8 Driver installation wizard

Figure 9 Driver installation completion

After connecting the EVAL-CED1Z via USB, the Found New Hardware Wizard initiates. When properly installed, the wizard confirms the evaluation board software is ready.

Figure 10 Found New Hardware Wizard notification

Figure 11 Evaluation board setup confirmation

Verify the board appears in Device Manager under ADI Development Tools.

Figure 12 Device Manager verification

Troubleshooting the Installation

If the driver installation failed, Windows shows a question mark for “Other devices” in Device Manager. This is usually caused by non-administrator installation. Re-install as administrator with full privileges.

Figure 13 Unrecognized device in Device Manager

Figure 14 Uninstalled USB device properties

Running the Evaluation Software

The evaluation software performs:

• Histogram for code transition noise (DC)

• FFT for SNR, SINAD, THD, and SFDR

• Decimation (digital filtering)

The software is located at: C:\Program Files\Analog Devices\PulSAR ADC Evaluation Software\Eval PulSAR CED.exe

It is also available in the Start menu under Analog Devices PulSAR Evaluation Software.

Software Operation

Starting the software opens the Raw Data Capture window.

Figure 15 Raw Data Capture setup screen

1. Click the arrow in the upper left corner to start.

2. Select the device (AD7944, AD7985, or AD7986).

3. Set the controls:

   • Sample Frequency: Enter rate in kHz (supports notation like “10k” for 10,000,000 Hz or “10 MSPS”).

   • Input Range: Select 4.096V or 5V for correct LSB display.

   • Interface Mode: Select Busy mode options.

   • Turbo CTRL: Select Turbo mode or normal mode.

   • CNV Mode: Select Continuous or burst conversion.

   • Coding: AD7986 uses “2 compl” (twos complement); AD7944/AD7985 use binary.

4. Control functions (top menu):

   • Save (F5): LV Config, HTML, or Spreadsheet options.

   • Stop (F10): Halt software.

   • RESET: Reset the CED capture board.

Context Help

Select Help > Show Context Help or press F1. Hovering over screen items displays context information.

Figure 16 On-screen help and histogram controls

Histogram and Oscilloscope Charts

Use the buttons to select single or continuous data capture. Enter the sample count in the “# of Samples (k)” field. Statistics display in the Histogram Data section; graphics display in the chart area. Results can be viewed as histogram or oscilloscope via tab selection. The “Summary” tab shows both charts together.

Figure 17 Histogram data window

Figure 18 Histogram chart display

Figure 19 Oscilloscope time-domain chart

Figure 20 Oscilloscope display tabs

Figure 21 Summary tab view

FFT Spectrum Data

Select the “Spectrum” tab in the Raw Data Capture window. The Spectrum Data section shows x-axis (frequency) and y-axis (magnitude) data.

Figure 22 FFT spectrum analysis window

Troubleshooting

Software Tips

• Install the software from the CD or website before connecting the hardware.

• Allow the full installation (two-part: software + drivers); a PC restart may be required.

• Let the Found New Hardware Wizard complete when first plugging in the USB.

• Verify board connection to the EVAL-CED1Z, daughter card connection, and Device Manager recognition.

Hardware Tips

If the software reads no data:

1. Verify the EVAL-CED1Z power and voltages on the P connectors.

2. Confirm signal source operation and expected signal output.

3. Probe the signal path points (driver amplifier inputs, ADC inputs).

For SNR performance issues:

• Some sources require filtering; the board was tested with the AP-2322 analyzer/source.

• Ensure the signal amplitude covers the full-scale ADC range.

• Monitor the max/min amplitude or fundamental in the Spectrum tab.

• Adjust the source for full-scale swing.

Design Resources

Complete design support files (schematics, Gerber files, bill of materials) and evaluation software are available for download from the respective evaluation board product pages on analog.com.

Related Links

Resource	Description
AD7944	14-bit, 2.5 MSPS ADC with internal reference
AD7985	16-bit, 2.5 MSPS ADC with internal reference
AD7986	18-bit, 2 MSPS differential input ADC with internal reference
AD8021	Low noise, high speed amplifier
AD8032	Low power, low noise amplifier
ADA4899-1	Low noise, high speed amplifier
ADR435	Ultralow noise XFET voltage reference
ADP1715	High accuracy low IQ 500 mA adjustable LDO regulator
ADP3334	500 mA low dropout CMOS linear regulator
EVAL-CED1Z	Converter evaluation and development board