
Timing Diagram
(Continued)
Functional Description
The ADC10030 maintains excellent dynamic performance
for input signals up to and exceeding half the clock fre-
quency. The use of an internal sample-and-hold amplifier
(SHA) enables sustained dynamic performance for signals of
input frequency beyond the clock rate, lowers the converter’s
input capacitance and reduces the number of external com-
ponents required.
The analog signal at V
that is within the voltage range set
by V
+ S and V
S are digitized to ten bits at up to
30 MSPS. Input voltages below V
S will cause the out-
put word to consist of all zeroes. Input voltages above
V
REF
+ S will cause the output word to consist of all ones.
V
+ S has a range of 2.6V to 3.8V, while V
S has a
range of 1.7V to 2.8V. V
REF
+ S should always be at least
1.0V more positive than V
REF
S.
Data is acquired at the falling edge of the clock and the digi-
tal equivalent of that data is available at the digital outputs
2.0 clock cycles plus t
OD
later. TheADC10030 will convert as
long as the clock signal is present at pin 9 and the PD pin is
low. The Output Enable pin (OE), when low, enables the out-
put pins. The digital outputs are in the high impedance state
when the OE pin or the PD pin is high.
Applications Information
1.0 THE ANALOG INPUT
The analog input of the ADC10030 is a switch (transmission
gate) followed by a switched capacitor amplifier. The capaci-
tance seen at the input changes with the clock level, appear-
ing as about 3 pF when the clock is low, and about 5 pF
when the clock is high. This small change in capacitance can
be reasonably assumed to be a fixed capacitance. Care
should be taken to avoid driving the input beyond the supply
rails, even momentarily, as during power-up.
The CLC409 has been found to be a good device to drive the
ADC10030 because of its wide bandwidth, low distortion and
minimal Differential Gain and Differential Phase. The
CLC409 performs best with a feedback resistor of about
100
.
Care should be taken to keep digital noise out of the analog
input circuitry to maintain highest noise performance.
2.0 REFERENCE INPUTS
Note:
Throughout this data sheet reference is made to V
+ and to V
.
These refer to the internal voltage across the reference ladder and are,
nominally, V
REF
+ S and V
REF
S, respectively.
Figure 4 shows a simple reference biasing scheme with
minimal components. While this circuit might suffice for
some applications, it does suffer from thermal drift because
the external will have a different temperature coefficient than
the on-chip resistors. Also, the on-chip resistors, while well
matched to each other, will have a large tolerance compared
with any external resistors, causing the value of V
REF
+ and
V
REF
to be somewhat variable.
The V
REF
+ F and V
REF
F pins should each be bypassed to
AGND with 10 μF tantalum or electrolytic capacitors and
0.1 μF ceramic capacitors.
The circuit of Figure 5 is an improvement over the circuit of
Figure 4in that the positive end of the reference ladder is de-
fined with a reference voltage. This reduces problems of
high reference variability and thermal drift.
In addition to the usual V
+F and V
F reference in-
puts, the ADC10030 has two sense outputs for precision
control of the ladder voltages. These sense outputs (V
+
S and V
S) compensate for errors due to IR drops be-
tween the source of the reference voltages and the ends of
the reference ladder itself.
With the addition of two op-amps, the voltages at the top and
bottom of the reference ladder can be forced to the exact
value desired, as shown in Figure 6
DS101064-17
FIGURE 2. AC Test Circuit
DS101064-16
FIGURE 3. t
EN
, t
DIS
Test Circuit
A
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