5962-9756301HXC View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'5962-9756301HXC' PDF : 16 Pages View PDF
AD9070
Figure 9 shows typical connections for the analog inputs when
using the AD9070 in a dc-coupled system with single-ended
signals. The AD820 is used to offset the ground referenced
input signal to the level required by the AD9070. A very high
performance amplifier, such as the AD9631, is required to avoid
degrading the analog signal presented to the ADC. A buffered
ac interface is easily implemented, with even fewer components
(Figure 10).
VIN
؎0.5V
RT
350⍀
0.1F
350⍀
+5V
AD9631
–5V
1k⍀ 1k⍀
AD820
–5V 0.1F 1k⍀
0.1F
–5V
VEE
AIN
GND
AD9070
AIN
VREF OUT
VREF IN
Figure 9. DC-Coupled Input
VIN
1Vp-p
RT
350⍀
0.1F
350⍀
+5V
0.1F
AD9631
–5V
500⍀
500⍀
0.1F
–5V
VEE GND
AIN
AD9070
AIN
0.1F
VREF OUT
VREF IN
Figure 10. AC-Coupled Input
Special care was taken in the design of the analog input section
of the AD9070 to prevent damage and corruption of data when
the input is overdriven. The nominal input range is –1.988 V
to –3.012 V (1.024 V p–p centered at –2.5 V). Out-of-range
comparators detect when the analog input signal is out of this
range and set the OR output signal HIGH. The digital out-
puts are locked at plus or minus full scale (1FFh or 200h) for
voltages that are out of range but between –1 V and –5 V. Input
voltages outside of this range may result in invalid codes at the
ADCs output.
When the analog input signal returns to the nominal range, the
out-of-range comparators return the ADC to its active mode
and the device recovers in approximately 3 ns.
The input is protected to one volt outside of the power supply
rails. For nominal power (–5 V and ground), the analog input
will not be damaged with signals ranging from –6.0 V to +1.0 V.
Voltage Reference
A stable and accurate –2.5 V voltage reference is built into the
AD9070 (VREF OUT) in the SOIC (BR) package. In normal
operation, the internal reference is used by strapping Pins 3
and 4 of the AD9070 together. The internal reference can
provide 100 µA of extra drive current that may be used for
other circuits.
Some applications may require greater accuracy, improved
temperature performance or adjustment of the gain of the
AD9070, which cannot be obtained by using the internal
reference. For these applications, an external –2.5 V reference
can be connected to VREF IN, which requires 5 µA of drive
current (Figure 11).
–5V
+VIN
AD780
VOUT
GND
1.25k⍀
NC
0.1F
VEE GND
VREF OUT
AD9070
VREF IN
–5V
Figure 11. Using the AD780 Voltage Reference
The input range can be adjusted by varying the reference voltage
applied to the AD9070. No appreciable degradation in perfor-
mance occurs when the reference is adjusted ± 4%. The full-
scale range of the ADC tracks reference voltage changes linearly.
Timing
The performance of the AD9070 is insensitive to the duty cycle
of the clock over a wide range of operating conditions: pulse-
width variations of as much as ± 20% will cause no degradation
in performance (see TPC 9).
The AD9070 provides latched data outputs, with three pipeline
delays. Data outputs are available one propagation delay (tPD)
after the rising edge of the encode command (Figure 1). The
length of the output data lines and loads placed on them should
be minimized to reduce transients within the AD9070; these
transients can detract from the converter’s dynamic performance.
The minimum guaranteed conversion rate of the AD9070 is
40 MSPS. At clock rates below 40 MSPS, dynamic performance
may degrade. The AD9070 will operate in bursts, but the user
must flush the internal pipeline each time the clock restarts.
Valid data will be produced on the fourth rising edge of the
ENCODE signal after the clock is restarted.
–10–
REV. C
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