–18–

REV. B

AD7569/AD7669

Figure 27. Typical DAC Output Voltages for Microstepping

and Direction Signals for Clockwise Rotation with the

UDN-2998W

ANALOG DELAY LINE—AD7569

In many applications, especially in audio systems, it is necessary

to provide a delay on the input signal. The circuit of Figure 28

shows how a simple analog delay line can be implemented,

based on the AD7569. The input signal is sampled using the

AD7569 ADC, and converted data is loaded into the 6116 (2K

8 static ram). The inverted input clock drives a counter that

selects the address for the 6116. The delay is selected by choos-

ing one of the output lines of the HCT4040 counter to reset the

coun-ter. This can be done using a simple switch in a manual

system or by a multiplexer in a programmable delay application.

Data is written to the DAC using the inverted input clock signal.

Figure 28. Analog Delay Line

the length of the delay is reached (i.e., until the counter is re-

set). From this point forward, the delayed data is read from the

6116 and loaded to the DAC before the newly converted data is

written into the same memory location. The input clock to the

system can be a square wave of maximum input frequency 200

kHz

(assuming 2

µs conversion time for the ADC). The mark/space

ratio of the input clock can be varied to maximize the sampling

frequency if required. The clock low time has to be equal to the

conversion time and access time of the ADC plus the setup time

required for the 6116. The clock high time has only to be equal

to the setup time for the DAC plus the delay time through the

counter and the access time of the 6116.

The amount of memory used, as well as the sampling frequency,

determines the maximum possible delay. Using the HCT4040,

and the 6116 with an input clock frequency of 200 kHz, the

maximum delay is 5 ms on a maximum input frequency of

100 kHz. Using 64K memory, with an 8 kHz input clock fre-

quency, the maximum delay is 8 seconds on a maximum input

frequency of 4 kHz.

TRANSIENT RECORDER—AD7569

The scheme just outlined can also form the basis for a transient

recorder. In this case, transients on the input signal are con-

verted and stored in memory. The transient can then be recalled

from memory at a later time, and the transient waveform can be

recreated using the AD7569 DAC.

INFINITE SAMPLE-AND-HOLD—AD7569

The AD7569 is ideal for implementing a single-chip infinite

sample-and-hold function. Basically, the ADC samples and con-

verts the input signal into an 8-bit digital word. The 8 bits of

data are then loaded to the DAC and the sampled value is re-

stored to analog form. The sampled value is held until the DAC

register is updated. The full-scale matching between the ADC

and the DAC on the AD7569 ensures a typical error of less than

1% between the analog input voltage and the “held” output

voltage. Figure 29 shows the connections required on the

AD7569 to achieve this infinite sample-and-hold function.

Figure 29. Infinite Sample-and-Hold