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Functional Description
The ADC10080 uses a pipeline architecture and has error
correction circuitry to help ensure maximum performance.
Differential analog input signals are digitized to 10 bits. In dif-
ferential mode each analog input signal should have a peak-
to-peak voltage equal to 1.0V, 0.75V or 0.5V, depending on
the state of the IRS pin (pin 5), and be centered around V
and be 180° out of phase with each other. If single ended
operation is desired, V
- may be tied to the V
IN
A single ended input signal may then be applied to V
should have a mid range value of V
should be 2.0V, 1.5V or 1.0V peak-to-peak, depending on the
state or the IRS pin (pin 5).
Applications Information
1.0 ANALOG INPUTS
The ADC10080 has two analog signal inputs, V
These two pins form a differential input pair. There is one
common mode pin V
COM
mode input voltage.
1.1 REFERENCE PINS
The ADC10080 is designed to operate with a 1.2V reference.
The voltages at V
, V
COM
REFT
reference voltage. It is very important that all grounds asso-
ciated with the reference voltage and the input signal make
connection to the analog ground plane at a single point to
minimize the effects of noise currents in the ground path. The
three Reference Bypass Pins V
made available for bypass purposes only. These pins should
each be bypassed to ground with a 0.1 µF capacitor. DO NOT
LOAD these pins.
1.2 V
PIN
COM
This pin supplies a voltage for possible use to set the common
mode input voltage. This pin may also be connected to V
so that V
+ may be used as a single ended input. This pin
IN
should be bypassed with at least a 0.1 uF capacitor. Do not
load this pin.
1.3 SIGNAL INPUTS
The signal inputs are V
IN
tude is defined as V
+ − V
IN
3:
FIGURE 3. Input Voltage Waveforms for a 2V
Differential Input
A single ended input signal is shown in Figure 4.
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pin (pin 4).
COM
IN
. The signal amplitude
COM
+ and V
IN
that may be used to set the common
, and V
are derived from the
REFB
, V
and V
REF
REFT
REFB
+ and V
−. The input signal ampli-
IN
− and is represented in Figure
IN
20048547
P-P
CM
+, and
FIGURE 4. Input Voltage Waveform for a 2V
The internal switching action at the analog inputs causes en-
ergy to be output from the input pins. As the driving source
tries to compensate for this, it adds noise to the signal. To
−.
IN
prevent this, use 18Ω series resistors at each of the signal
input pins with a 25 pF capacitor across the inputs, as shown
in Figure 5. These components should be placed close to the
ADC because the input pins of the ADC is the most sensitive
part of the system and this is the last opportunity to filter the
input. The two 18Ω resistors and the 25 pF capacitor form a
low-pass filter with a -3 dB frequency of 177 MHz.
1.4 CLK PIN
The CLK signal controls the timing of the sampling process.
Drive the clock input with a stable, low jitter clock signal in the
frequency range indicated in the AC Electrical Characteristics
, are
Table with rise and fall times of less than 2 ns. The trace car-
rying the clock signal should be as short as possible and
should not cross any other signal line, analog or digital, not
even at 90°. The CLK signal also drives an internal state ma-
chine. If the CLK is interrupted, or its frequency is too low, the
charge on internal capacitors can dissipate to the point where
the accuracy of the output data will degrade. This is what limits
-,
IN
the lowest sample rate. The duty cycle of the clock signal can
affect the performance of any A/D Converter. Because
achieving a precise duty cycle is difficult, the ADC10080 is
designed to maintain performance over a range of duty cy-
cles. While it is specified and performance is guaranteed with
a 50% clock duty cycle, performance is typically maintained
with minimum clock low and high times indicated in the AC
Electrical Characteristics Table. Both minimum high and low
times may not be held simultaneously.
1.5 STBY PIN
The STBY pin, when high, holds the ADC10080 in a power-
down mode to conserve power when the converter is not
being used. The power consumption in this state is 15 mW.
The output data pins are undefined in this mode. Power con-
sumption during power-down is not affected by the clock
frequency, or by whether there is a clock signal present. The
data in the pipeline is corrupted while in power down.
1.6 DF PIN
The DF (Data Format) pin, when high, forces the ADC10080
to output the 2's complement data format. When DF is tied
low, the output format is offset binary.
1.7 IRS PIN
The IRS (Input Range Select) pin defines the input signal am-
plitude that will produce a full scale output. The table below
describes the function of the IRS pin.
16
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Ended Input
Single
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