AD7569/AD7669
On initial start-up, the output voltage, VO, will be invalid until
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.
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
ϫ 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.
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
Figure 28. Analog Delay Line
REV. B
–18–
ADI [ ADI ]
