AD9051-2VPCB AD [Analog Devices], AD9051-2VPCB Datasheet - Page 9

• Manufacturer Part Number: AD9051-2VPCB
• Description: 10-Bit, 60 MSPS A/D Converter
• Manufacturer: AD [Analog Devices]

THEORY OF OPERATION
Refer to the block diagram on the front page.
The AD9051 employs a subranging architecture with digital
error correction. This combination of design techniques ensures
true 10-bit accuracy at the digital outputs of the converter.
At the input, the analog signal is buffered by a high speed differ-
ential buffer and applied to a track-and-hold (T/H) that holds
the analog value present when the unit is strobed with an
ENCODE command. The conversion process begins on the
rising edge of this pulse. The two stage architecture completes a
coarse and then a fine conversion of the T/H output signal.
Error correction and decode logic correct and align data from
the two conversions and present the result as a 10-bit parallel
digital word. Output data are strobed on the rising edge of the
ENCODE command. The subranging architecture results in five
pipeline delays for the output data. Refer to the AD9051 Timing
Diagram.
USING THE AD9051
3 V System
The digital input and outputs of the AD9051 can be easily
configured to directly interface to 3 V logic systems. The encode
input (Pin 13) is TTL compatible with a logic threshold of
1.5 V. This input is actually a CMOS stage (refer to Equivalent
Encode Input Stage) with a TTL threshold, allowing operation
with TTL, CMOS and 3 V CMOS logic families. Using 3 V
CMOS logic allows the user to drive the encode directly without
the need to translate to +5 V. This saves the user power and
board space. As with all high speed data converters, the clock
signal must be clean and jitter free to prevent the degradation of
dynamic performance.
The AD9051 outputs can also directly interface to 3 V logic
systems. The digital outputs are standard CMOS stages (refer to
AD9051 Output Stage) with isolated supply pins (Pins 20, 22
V
levels vary respectively. By connecting Pins 20 and 22 to the
3 V logic supply, the AD9051 will supply 3 V output levels.
Care should be taken to filter and isolate the output supply of
the AD9051 as noise could be coupled into the ADC, limiting
performance.
Analog Input
The analog input of the AD9051 is a differential input buffer
(refer to AD9051 Equivalent Analog Input). The differential
inputs are internally biased at +2.5 V, obviating the need for
external biasing. Excellent performance is achieved whether the
analog inputs are driven single-endedly or differentially (for best
dynamic performance, impedances at AIN and AINB should
match).
Figure 21 shows typical connections for the analog inputs when
using the AD9051 in a dc coupled system with single-ended
signals. All components are powered from a single +5 V supply.
The AD820 is used to offset the ground referenced input signal
to the level required by the AD9051.
AC coupling of the analog inputs of the AD9051 is easily accom-
plished. Figure 22 shows capacitive coupling of a single-ended
signal while Figure 23 shows transformer coupling differentially
into the AD9051.
REV. A
DD
). By varying the voltage on the V
DD
pins, the digital output
–9–
The AD830 provides a unique method of providing dc level
shift for the analog input. Using the AD830 allows a great deal
of flexibility for adjusting offset and gain. Figure 24 shows the
AD830 configured to drive the AD9051. The offset is provided
by the internal biasing of the AD9051 differential input (Pin 9).
For more information regarding the AD830, see the AD830
data sheet.
Figure 22. Single-Ended, Capacitively-Coupled AD9051
Figure 23. Differentially Driven AD9051 Using Trans-
former Coupling
Figure 21. Single Supply, Single-Ended, DC-Coupled
AD9051
–0.625V
+0.625V
–0.625V
+0.625V
V
TO
V
TO
IN
IN
+0.625V
–0.625V
Figure 24. Level-Shifting with the AD830
–0.625V
+0.625V
V
TO
V
IN
TO
IN
140
0.1 F
1k
140
140
140
+5V
–5V
2
3
4
1
1k
AD830
AD9631
+5V
140
140
+5V
–5V
+15V
–5V
AD820
AD9631
AD9631
0.1 F
7
+5V
50
0.1 F
0.1 F
0.1 F
T1-1T
9
10
10
9
10
9
0.1 F
AD9051
10
AD9051
AD9051
AD9051
9
+5V
+5V
+5V
AD9051
+5V