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PDF ADS944 Data sheet ( Hoja de datos )
| Número de pieza | ADS944 | |
| Descripción | 14-Bit/ 5MHz Sampling A/D Converters | |
| Fabricantes | ETC | |
| Logotipo |  |
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®®
FEATURES
• 14-bit resolution
• 5MHz minimum sampling rate
• No missing codes over full military temperature range
• Edge-triggered, no pipeline delay
• Low power, 2.95 Watts
• Small, 32-pin, ceramic TDIP package
• SMT package available
• Excellent dynamic performance
• MIL-STD-883 screening or DESC SMD available
GENERAL DESCRIPTION
The low-cost ADS-944 is a high-performance, 14-bit, 5MHz
sampling A/D converter. This device accurately samples full-
scale input signals up to Nyquist frequencies with no missing
codes. The dynamic performance of the ADS-944 has been
optimized to achieve a THD of –77dB and a SNR of 76dB.
Packaged in a small, 32-pin TDIP, the functionally complete
ADS-944 contains a fast-settling sample-hold amplifier, a
subranging (two-pass) A/D converter, an internal reference,
timing and control logic, three-state outputs, and error-
correction circuitry. Digital input and output levels are TTL.
Requiring ±15V, +5V and –5.2V supplies, the ADS-944
typically dissipates 2.95 Watts. The unit is offered with a
bipolar input range of ±1.25V. Models are available for use in
either commercial (0 to +70°C) or military (–55 to +125°C)
operating temperature ranges. Typical applications include
radar signal analysis, medical/graphic imaging, and
FFT spectrum analysis.
ADS-944
14-Bit, 5MHz
Sampling A/D Converters
INPUT/OUTPUT CONNECTIONS
PIN FUNCTION
PIN FUNCTION
1 +5V ANALOG SUPPLY 32 START CONVERT
2 –5.2V DIGITAL SUPPLY 31 BIT 1 (MSB)
3 ANALOG INPUT
30 BIT 1 (MSB)
4 ANALOG GROUND
29 BIT 2
5 OFFSET ADJUST
28 BIT 3
6 ANALOG GROUND
27 BIT 4
7 GAIN ADJUST
26 BIT 5
8 COMP. BITS
25 BIT 6
9 OUTPUT ENABLE
24 BIT 7
10 +5V DIGITAL SUPPLY 23 BIT 8
11 ANALOG GROUND
22 BIT 9
12 +15V SUPPLY
21 BIT 10
13 –15V SUPPLY
20 BIT 11
14 –5.2V ANALOG SUPPLY 19 BIT 12
15 DIGITAL GROUND
18 BIT 13
16 EOC
17 BIT 14 (LSB)
ANALOG INPUT 3
GAIN ADJUST 7
OFFSET ADJUST 5
START CONVERT 32
EOC 16
–
S/H
+
GAIN
CIRCUIT
BUFFER
FLASH
ADC
1
REF
Σ
DAC
OFFSET
CIRCUIT
AMP
FLASH
ADC
2
TIMING AND
CONTROL LOGIC
31 BIT 1 (MSB)
30 BIT 1 (MSB)
29 BIT 2
28 BIT 3
27 BIT 4
26 BIT 5
25 BIT 6
24 BIT 7
23 BIT 8
22 BIT 9
21 BIT 10
20 BIT 11
19 BIT 12
18 BIT 13
17 BIT 14 (LSB)
9 OUTPUT ENABLE
1
+5V
ANALOG
SUPPLY
2
–5.2V
DIGITAL
SUPPLY
4, 6, 11
ANALOG
GROUND
10
+5V
DIGITAL
SUPPLY
12
+15V
SUPPLY
14
–5.2V
ANALOG
SUPPLY
Figure 1. ADS-944 Functional Block Diagram
15
DIGITAL
GROUND
8
COMP.
BITS
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
1 page  
®®
ADS-944
Table 1. Output Coding
MSB
OUTPUT CODING
LSB MSB
LSB MSB
INPUT RANGE BIPOLAR
LSB
±1.25V
SCALE
111111 1111 1111
11 1000 0000 0000
11 0000 0000 0000
10 0000 0000 0000
01 0000 0000 0000
00 1000 0000 0000
00 0000 0000 0001
00 0000 0000 0000
OFF. BINARY
00 0000 0000 0000
00 1111 1111 1111
00 1111 1111 1111
01 1111 1111 1111
10 1111 1111 1111
11 0111 1111 1111
11 1111 1111 1110
11 1111 1111 1111
COMP. OFF. BIN.
01 1111 1111 1111
01 1000 0000 0000
01 0000 0000 0000
00 0000 0000 0000
11 0000 0000 0000
10 1000 0000 0000
10 0000 0000 0001
10 0000 0000 0000
TWO'S COMP.
+1.249847
+0.937500
+0.625000
0.000000
–0.625000
–0.937500
–1.249847
–1.250000
+FS –1 LSB
+3/4 FS
+1/2FS
0
–1/2FS
–3/4FS
–FS +1 LSB
–FS
TIMING
The ADS-944 is an edge-triggered device. A conversion is
initiated by the rising edge of the start convert pulse and no
additional external timing signals are required. The device
does not employ "pipeline" delays to increase its throughput
rate. It does not require multiple start convert pulses to bring
valid digital data to its output pins.
Approximately 10ns after the rising edge of the start convert
signal, the ADS-944's internal sample-hold amplifier is driven
into the hold mode by the internal S/H control line. After a
35ns delay to allow for S/H output transient settling, the
conversion process begins, and the EOC line (pin 16) is driven
high. The complete A/D conversion requires approximately
150ns. The falling of EOC signals that the conversion is now
complete and digital output data is now valid.
This device actually guarantees that digital output data will be
valid for 10ns prior to the falling edge of EOC. Therefore, EOC
can be used to latch data into external registers that have
appropriate setup times. Any other available timing edges,
including a delayed EOC or the rising edge of the next EOC
pulse, can also be used for this purpose.
The falling edge of the start convert pulse, though irrelevant to
device timing, can cause conversion errors if it occurs at
certain times. Therefore, the recommended start convert
pulse width is between 40 and 80ns or between 130 and
160ns. DATEL performs ADS-944 production testing at the full
5MHz sampling rate using 80ns start convert pulses.
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 (TA = +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.
START
CONVERT
N
80ns typ.
N+1
INTERNAL S/H
EOC
10ns typ.
115ns typ.
Hold
35ns typ.
Acquisition Time
90ns max.
Hold
60ns typ., ±10ns
Conversion Time
150ns typ., 160ns max.
OUTPUT
DATA
50ns typ., 60ns max.
DATA (N-1) VALID
INVALID
DATA
140ns min., 150ns typ.
DATA N VALID
Note: Scale is approximately 10ns per division.
START CONVERT pulse width: 40 to 80ns or 130 to 160ns.
Figure 3. ADS-944 Timing Diagram
5
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| PDF Descargar | [ Datasheet ADS944.PDF ] | |
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