REV. 0

–14–

AD8600

The functionality of this circuit is shown in the scope photo in

Figure 24 The top trace is the control ramp, which goes from

0 V to 1.25 V. The bottom trace is the output of the AD600.

The input is actually a 12 mV p-p, 10 kHz sine wave. Thus, the

bottom trace shows the envelop of this waveform to illustrate

the increase in gain as time progresses. This ramp was gener-

ated under control of the 68HC11 using the “ramp” subroutine

as mentioned above. The slope of the ramp can easily be

lengthened by adding some delay in the loop, or the slope can

be increased by stepping by 2 or more LSBs instead of the cur-

rent 1 LSB changes.

GAIN

CONTROL

1V/DIV

AD600

OUTPUT

0.2V/DIV

200µs/DIV

Figure 24. Time Dependent Gain of the AD600

Glitch Impulse

A specification of interest in many DAC applications is the

glitch impulse. This is the amount of energy contained in any

overshoot when a DAC changes at its major carry transition, in

other words, when the DAC switches from code 01111111 to

code 10000000. This point is the most demanding because all

of the R-2R ladder switches are changing state. The AD8600’s

glitch impulse is shown in Figure 25. Calculating the value of

the glitch is accomplished by calculating the area of the pulse,

which for the AD8600 is: Glitch Impulse = (1/2)

× (100 mV) ×

(200 ns) = 10 nV sec.

200ns/DIV

200ns/DIV

50mV/DIV

Figure 25. Glitch Impulse