REV. B

AD9501

–10–

Analog Settling Time Measurement

The circuit shown in Figure 11 functions in a manner similar to

the digital delay detector; for this application, the clock must

be repetitive also. As in the delay detector, AD9501 #1 is used

to cancel the propagation delay of AD9501 #2, propagation

delay of the comparators, and stray delays. To accomplish this,

use the calibration procedure described earlier for the digital

delay generator.

The difference between the two circuits is in the detection method.

The register of the digital delay is replaced by a window com-

parator for the analog settling measurement.

around the final value of the DUT output signal. As shown in

the lower portion of the diagram, the output of the detector is

HIGH when the analog output signal of the converter is within

Therefore, the settling time can be measured by starting the delay

of AD9501 #2 at its maximum setting and decrementing it until

the window comparator goes low. The difference between the

DAC codes applied to AD9501 #2 and AD9501 #1 is a measure

of the settling time of the D/A converter being tested.

TRIGGER

AD9501 #1

DIGITAL

DATA

LATCH

OUTPUT

RESET

TRIGGER

AD9501 #2

LATCH

RESET

OUTPUT

DIGITAL

DATA

8

CLOCK IN

GROUND

8

D/A CONVERTER

UNDER TEST

OUTPUT

LOGIC

OUTPUT

Figure 11. Analog Settling Time Measurement

Layout Considerations

Although the inputs and output of the AD9501 are digital, the

delay is determined by analog circuits. This makes it critical to

use high speed analog circuit layout techniques to achieve rated

performance.

The ground plane should be on the component side of the

board and extend under the AD9501 to shield it from digital

switching signals. Most socket assemblies add significant

inter-lead capacitance and should be avoided whenever possible.

If sockets must be used, individual pin sockets, such as TYCO

part numbers 5-330808-3 (closed end) or 5-330808-6 (open end),

should be used.

Power supply decoupling is also critical for high speed design; a

0.1

mF capacitor should be connected as close as possible to

each supply pin.

OBSOLETE