ADS-927

14-Bit, 1MHz, Low-Power

Sampling A/D Converters

FEATURES

14-bit resolution

1MHz sampling rate

Functionally complete

No missing codes

Small 24-pin DDIP or SMT package

Low power, 1.9 Watts maximum

Operates from ±15V or ±12V supplies

Bipolar ±5V input range

GENERAL DESCRIPTION

The ADS-927 is a high-performance, 14-bit, 1MHz sampling
A/D converter. This device samples input signals up to Nyquist
frequencies with no missing codes. The ADS-927 features
outstanding dynamic performance including a THD of 80dB.

Housed in a small 24-pin DDIP or SMT (gull-wing) package,
the functionally complete ADS-927 contains a fast-settling
sample-hold amplifier, a subranging (two-pass) A/D converter,
a precise voltage reference, timing/control logic, and error-
correction circuitry. Digital input and output levels are TTL.

Requiring ±15V (or ±12V) and +5V supplies, the ADS-927
dissipates only 1.95W (1.65W for ±12V), maximum. The unit is
offered with a bipolar input (5V to +5V). Models are available
for use in either commercial (0 to +70°C) or military (55 to
+125°C) operating temperature ranges. Applications include
radar, sonar, spectrum analysis, and graphic/medical imaging.

INPUT/OUTPUT CONNECTIONS

PIN

FUNCTION

PIN

FUNCTION

BIT 14 (LSB)

12V/15V SUPPLY

BIT 13

ANALOG GROUND

BIT 12

+12V/+15V SUPPLY

BIT 11

+10V REFERENCE OUT

BIT 10

ANALOG INPUT

BIT 9

ANALOG GROUND

BIT 8

BIT 1 (MSB)

BIT 7

BIT 2

BIT 6

START CONVERT

BIT 5

EOC

BIT 4

DIGITAL GROUND

BIT 3

+5V SUPPLY

Figure 1. ADS-927 Functional Block Diagram

DATEL, Inc., 11 Cabot Boulevard, Mansfield, MA 02048-1151 (U.S.A.)

Tel: (508) 339-3000 Fax: (508) 339-6356

For immediate assistance: (800) 233-2765

REF

I
S

18 BIT 1 (MSB)

17 BIT 2

12 BIT 3

11 BIT 4

10 BIT 5

9 BIT 6

8 BIT 7

7 BIT 8

6 BIT 9

5 BIT 10

4 BIT 11

3 BIT 12

2 BIT 13

1 BIT 14 (LSB)

TIMING AND

CONTROL LOGIC

+10V REF. OUT 21

START CONVERT 16

EOC 15

I
G

I
T

I
O

I
C

DAC

FLASH

ADC

BUFFER

S/H

ANALOG INPUT 20

+5V SUPPLY

+12V/+15V SUPPLY

19, 23

ANALOG GROUND

DIGITAL GROUND

12V/15V SUPPLY

ADS-927

ABSOLUTE MAXIMUM RATINGS

PARAMETERS

LIMITS

UNITS

+12V/+15V Supply (Pin 22)

0 to +16

Volts

12V/15V Supply (pin 24)

0 to 16

Volts

+5V Supply (Pin 13)

0 to +6

Volts

Digital Input (Pin 16)

0.3 to +V

+0.3

Volts

Analog Input (Pin 20)

±15

Volts

Lead Temperature (10 seconds)

+300

°C

PHYSICAL/ENVIRONMENTAL

PARAMETERS

MIN.

TYP.

MAX.

UNITS

Operating Temp. Range, Case

ADS-927MC, GC

+70

°C

ADS-927MM, GM, 883

+125

°C

Thermal Impedance

°C/Watt

Storage Temperature

+150

°C

Package Type

24-pin, metal-sealed, ceramic DDIP or SMT

Weight

0.42 ounces (12 grams)

+25°C

0 to +70°C

55 to +125°C

ANALOG INPUT

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

UNITS

Input Voltage Range

±5

Volts

Input Resistance

Input Capacitance

DIGITAL INPUT

Logic Levels

Logic "1"

+2.0

Volts

Logic "0"

+0.8

Volts

Logic Loading "1"

+20

µA

Logic Loading "0"

µA

Start Convert Positive Pulse Width

175

200

225

175

200

225

175

200

225

STATIC PERFORMANCE

Resolution

Bits

Integral Nonlinearity (f

= 10kHz)

±0.5

±0.75

±1.5

LSB

Differential Nonlinearity (f

= 10kHz)

±0.5

±0.95

±0.5

±0.95

±0.75

±0.99

LSB

Full Scale Absolute Accuracy

±0.08

±0.15

±0.25

±0.3

±0.5

%FSR

Bipolar Zero Error (Tech Note 2)

±0.05

±0.1

±0.25

±0.15

±0.3

%FSR

Bipolar Offset Error (Tech Note 2)

±0.05

±0.1

±0.25

±0.4

%FSR

Gain Error (Tech Note 2)

±0.1

±0.15

±0.25

±0.4

No Missing Codes (f

= 10kHz)

Bits

DYNAMIC PERFORMANCE

Peak Harmonics (0.5dB)

dc to 100kHz

100kHz to 500kHz

Total Harmonic Distortion (0.5dB)

dc to 100kHz

100kHz to 500kHz

Signal-to-Noise Ratio

(w/o distortion, 0.5dB)
dc to 100kHz

100kHz to 500kHz

Signal-to-Noise Ratio

(& distortion, 0.5dB)
dc to 100kHz

100kHz to 500kHz

Two-Tone Intermodulation

Distortion (f

= 100kHz,

240kHz, f

= 1MHz, 0.5dB)

Noise

350

µVrms

Input Bandwidth (3dB)

Small Signal (20dB input)

MHz

Large Signal (0.5dB input)

MHz

Feedthrough Rejection (f

= 500kHz)

Slew Rate

±60

V/µs

Aperture Delay Time

±20

Aperture Uncertainty

ps rms

S/H Acquisition Time

(to ±0.003%FSR, 10V step)

335

390

445

335

390

445

335

390

445

Overvoltage Recovery Time

400

1000

400

1000

400

1000

A/D Conversion Rate

MHz

FUNCTIONAL SPECIFICATIONS

= +25°C, ±V

= ±15V (or ±12V), +V

= +5V, 1MHz sampling rate, and a minimum 1 minute warmup unless otherwise specified.)

ADS-927

+25°C

0 to +70°C

55 to +125°C

ANALOG OUTPUT

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

UNITS

Internal Reference

Voltage

+9.95

+10.0

+10.05

+9.95

+10.0

+10.05

+9.95

+10.0

+10.05

Volts

Drift

±5

ppm/°C

External Current

1.5

DIGITAL OUTPUTS

Logic Levels

Logic "1"

+2.4

Volts

Logic "0"

+0.4

Volts

Logic Loading "1"

Logic Loading "0"

Delay, Falling Edge of EOC

to Output Data Valid

Output Coding

Offset Binary

POWER REQUIREMENTS, ±15V

Power Supply Ranges

+15V Supply

+14.5

+15.0

+15.5

+14.5

+15.0

+15.5

+14.5

+15.0

+15.5

Volts

15V Supply

14.5

15.0

15.5

14.5

15.0

15.5

14.5

15.0

15.5

Volts

+5V Supply

+4.75

+5.0

+5.25

+4.75

+5.0

+5.25

+4.75

+5.0

+5.25

Volts

Power Supply Currents

+15V Supply

+43

+65

+43

+65

+43

+65

15V Supply

+5V Supply

+71

+80

+71

+80

+71

+80

Power Dissipation

1.6

1.95

1.6

1.95

1.6

1.95

Watts

Power Supply Rejection

±0.02

%FSR/%V

POWER REQUIREMENTS, ±12V

Power Supply Ranges

+12V Supply

+11.5

+12.0

+12.5

+11.5

+12.0

+12.5

+11.5

+12.0

+12.5

Volts

12V Supply

11.5

12.0

12.5

11.5

12.0

12.5

11.5

12.0

12.5

Volts

+5V Supply

+4.75

+5.0

+5.25

+4.75

+5.0

+5.25

+4.75

+5.0

+5.25

Volts

Power Supply Currents

+12V Supply

+42

+65

+42

+65

+42

+65

12V Supply

+5V Supply

+71

+80

+71

+80

+71

+80

Power Dissipation

1.4

1.65

1.4

1.65

1.4

1.65

Watts

Power Supply Rejection

±0.02

%FSR/%V

6.02

(SNR + Distortion) 1.76 + 20 log

Full Scale Amplitude

Actual Input Amplitude

Effective bits is equal to:

This is the time required before the A/D output data is valid after the analog input
is back within the specified range.

Footnotes:

All power supplies must be on before applying a start convert pulse. All supplies
and the clock (START CONVERT) must be present during warmup periods. The
device must be continuously converting during this time. There is a slight
degradation in performance when using ±12V supplies.

See Ordering Information for 0 to +10V input range. Contact DATEL for
availability of other input voltage ranges.

A 1MHz clock with a 200ns wide start convert pulse is used for all production
testing. For applications requiring less than a 1MHz sampling rate, wider start
convert pulses can be used. See Timing Diagram for more details.

TECHNICAL NOTES

1. Obtaining fully specified performance from the ADS-927

requires careful attention to pc-card layout and power
supply decoupling. The device's analog and digital ground
systems are connected to each other internally. For optimal
performance, tie all ground pins (14, 19 and 23) directly to
a large analog ground plane below the package.

Bypass all power supplies and the REFERENCE OUTPUT
(pin 21) to ground with 4.7µF tantalum capacitors in parallel
with 0.1µF ceramic capacitors. Locate the bypass capaci-
tors as close to the unit as possible. If the user-installed
offset and gain adjusting circuit in Figure 2 is used, also
locate it as close to the ADS-927 as possible.

2. The ADS-927 achieves its specified accuracies without the

need for external calibration. If required, the device's small
initial offset and gain errors can be reduced to zero using
the input circuit of Figure 2. When using this circuit, or any
similar offset and gain-calibration hardware, make adjust-
ments following warmup. To avoid interaction, always
adjust offset before gain.

3. When operating the ADS-927 from ±12V supplies, do not

drive external circuitry with the REFERENCE OUTPUT. The
reference's accuracy and drift specifications may not be
met, and loading the circuit may cause accuracy errors
within the converter.

4. Applying a start convert pulse while a conversion is in

progress (EOC = logic "1") initiates a new and inaccurate
conversion cycle. Data for the interrupted and subsequent
conversions will be invalid.

ADS-927

CALIBRATION PROCEDURE

(Refer to Figures 2 and 3)

Any offset and/or gain calibration procedures should not be
implemented until devices are fully warmed up. To avoid
interaction, offset must be adjusted before gain. The ranges of
adjustment for the circuit of Figure 2 are guaranteed to
compensate for the ADS-927's initial accuracy errors and may
not be able to compensate for additional system errors.

All fixed resistors in Figure 2 should be metal-film types, and
multiturn potentiometers should have TCR's of 100ppm/°C or
less to minimize drift with temperature.

A/D converters are calibrated by positioning their digital
outputs exactly on the transition point between two adjacent
digital output codes. This can be accomplished by connecting
LED's to the digital outputs and adjusting until certain LED's
"flicker" equally between on and off. Other approaches
employ digital comparators or microcontrollers to detect when
the outputs change from one code to the next.

For the ADS-927, offset adjusting is normally accomplished at
the point where the MSB is a 1 and all other output bits are 0's
and the LSB just changes from a 0 to a 1. This digital output
transition ideally occurs when the applied analog input is
+½LSB (+305µV).

Gain adjusting is accomplished when all bits are 1's and the
LSB just changes from a 1 to a 0. This transition ideally
occurs when the analog input is at +full scale minus 1½ LSB's
(+4.999085V).

Zero/Offset Adjust Procedure

1. Apply a train of pulses to the START CONVERT input

(pin 16) so the converter is continuously converting. If
using LED's on the outputs, a 200kHz conversion rate will
reduce flicker.

2. Apply +305µV to the ANALOG INPUT (pin 20).

3. Adjust the offset potentiometer until the output bits are

a 1 and all 0's and the LSB flickers between 0 and 1.

Gain Adjust Procedure

1. Apply +4.999085V to the ANALOG INPUT (pin 20).

2. Adjust the gain potentiometer until the output bits are all 1's

and the LSB flickers between 1 and 0.

INPUT VOLTAGE

ZERO ADJUST

GAIN ADJUST

RANGE

+½ LSB

+FS 1½ LSB

±5V

+305µV

+4.999085V

Table 1. Zero and Gain Adjust

OUTPUT CODING

INPUT RANGE

BIPOLAR

MSB

LSB

±5V

SCALE

11 1111 1111 1111

+4.99939

+FS 1 LSB

11 1000 0000 0000

+3.75000

+3/4 FS

11 0000 0000 0000

+2.50000

+1/2FS

10 0000 0000 0000

0.00000

01 0000 0000 0000

2.50000

1/2FS

00 1000 0000 0000

3.75000

3/4FS

00 0000 0000 0001

4.99939

FS +1 LSB

00 0000 0000 0000

5.00000

Table 2. Output Coding

Figure 3. Typical ADS-927 Connection Diagram

Figure 2. ADS-927 Calibration Circuit

Coding is offset binary; 1LSB = 610µV.

To Pin 20
of ADS-927

15V

SIGNAL

INPUT

GAIN

ADJUST

1.98k

+15V

1.2M

20k

15V

+15V

ZERO/

OFFSET
ADJUST

ADS-927

BIT 1 (MSB)

BIT 2

BIT 3

BIT 4

BIT 5

BIT 6

BIT 7

BIT 8

BIT 9

BIT 10

BIT 11

BIT 12

BIT 13

BIT 14 (LSB)

EOC

ANALOG
INPUT

START

CONVERT

19, 23

0.1µF

4.7µF

+5V

0.1µF

4.7µF

0.1µF

4.7µF

12V/15V

+12V/+15V

0.1µF

4.7µF

21 +10V REF. OUT

DIGITAL
GROUND

0 to +10V

ANALOG
GROUND

ADS-927

THERMAL REQUIREMENTS

All DATEL sampling A/D converters are fully characterized and
specified over operating temperature (case) ranges of
0 to +70°C and 55 to +125°C. All room-temperature
(T

= +25°C) production testing is performed without the use of

heat sinks or forced-air cooling. Thermal impedance figures
for each device are listed in their respective specification
tables.

These devices do not normally require heat sinks, however,
standard precautionary design and layout procedures should
be used to ensure devices do not overheat. The ground and
power planes beneath the package, as well as all pcb signal
runs to and from the device, should be as heavy as possible to
help conduct heat away from the package.

Electrically-insulating, thermally-conductive "pads" may be
installed underneath the package. Devices should be
soldered to boards rather than "socketed", and of course,
minimal air flow over the surface can greatly help reduce the
package temperature.

In more severe ambient conditions, the package/junction
temperature of a given device can be reduced dramatically
(typically 35%) by using one of DATEL's HS Series heat sinks.
See Ordering Information for the assigned part number. See
page 1-183 of the DATEL Data Acquisition Components
Catalog for more information on the HS Series. Request
DATEL Application Note AN-8, "Heat Sinks for DIP Data
Converters", or contact DATEL directly, for additional
information.

Figure 4. ADS-927 Timing Diagram

Notes: 1. f

= 1MHz.

2. The ADS-927 is a pulse-triggered device. Its internal operations

are triggered by both the rising and falling edges of the start
convert pulse. When sampling at 1MHz, the start pulse must be
between 175 and 225nsec wide. For lower sampling rates, wider
start pulses may be used, however, a minimum pulse width low of
50nsec must be maintained.

START

CONVERT

OUTPUT

DATA

INTERNAL S/H

N + 1

Data (N 1) Valid

Acquisition Time

10ns

typ.

Data N Valid (850ns min.)

EOC

Conversion Time

Invalid

Data

150ns max.

10ns typ.

390ns ±55ns

35ns max.

Hold

200ns
±25ns

610ns typ.

480ns ±20ns

70ns ±10ns

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