adc1204006 National Semiconductor Corporation, adc1204006 Datasheet - Page 13

• Manufacturer Part Number: adc1204006
• Description: 12-bit, 40 Msps, 340 Mw A/d Converter With Internal Sample-and-hold
• Manufacturer: National Semiconductor Corporation

Functional Description
Operating on a single +5V supply, the ADC12040 uses a
pipeline architecture and has error correction circuitry to help
ensure maximum performance. The differential analog input
signal is digitized to 12 bits.
The reference input is buffered to ease the task of driving
that pin and the output word rate is the same as the clock
frequency. The analog input voltage is acquired at the rising
edge of the clock and the digital data for a given sample is
delayed by the pipeline for 6 clock cycles. A logic high on the
power down (PD) pin reduces the converter power con-
sumption to 40 mW.
Applications Information
1.0 OPERATING CONDITIONS
We recommend that the following conditions be observed for
operation of the ADC12040:
V
within the limits of 0V to V
1.1 Analog Inputs
The ADC12040 has two signal input pins, V
forming a differential input pair, and one reference input pin,
V
1.2 Reference Pins
The ADC12040 is designed to operate with a 2.0V reference,
but performs well with reference voltages in the range of
1.0V to 2.2V. Lower reference voltages will decrease the
signal-to-noise ratio (SNR). Increasing the reference voltage
(and the input signal swing) beyond 2.2V will degrade THD
for a full-scale input. It is important that all grounds associ-
ated with the reference voltage and the input signal make
connection to the 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.
1.3 Signal Inputs
The signal inputs are V
defined as
Figure 2 shows the expected input signal range.
Note that the common mode input voltage range is 1V to 3V
with a nominal value of V
main between ground and 4V.
The Peaks of the individual input signals (V
should each never exceed the voltage described as
to maintain THD and SINAD performance.
REF
REF
4.75V ≤ V
V
2.35V ≤ V
100 kHz ≤ f
1.0V ≤ V
0.5V ≤ V
0V ≤ V
D
.
= V
and V
A
IN
REF
CM
≤ (V
CM
A
DR
V
CLK
≤ 5.25V
≤ 3.0V
IN
≤ 2.2V
must be such that the signal swing remains
≤ V
A
+, V
− 1.0V)
≤ 50 MHz
D
V
IN
IN
− = V
IN
= (V
+ and V
A
A
.
IN
/2. The input signals should re-
REF
+) – (V
/2 + V
IN
−. The input signal, V
IN
RP
CM
−)
, V
≤ 4V
RM
IN
IN
and V
+ and V
+ and V
RN
) are
IN
IN
IN
, is
−,
−)
13
The ADC12040 performs best with a differential input with
each input centered around a V
age swing at V
value of the reference voltage or the output data will be
clipped. The two input signals should be exactly 180˚ out of
phase from each other and of the same amplitude. For single
frequency inputs, angular errors result in a reduction of the
effective full scale input. For a complex waveform, however,
angular errors will result in distortion.
For angular deviations of up to 10 degrees from these two
signals being 180 out of phase, the full scale error in LSB
can be described as approximately
Where dev is the angular difference between the two signals
having a 180˚ relative phase relationship to each other (see
Figure 3). Drive the analog inputs with a source impedance
less than 100Ω.
For differential operation, each analog input signal should
have a peak-to-peak voltage equal to the input reference
voltage, V
TABLE 1. Input to Output Relationship – Differential
V
V
V
V
FIGURE 3. Angular Errors Between the Two Input
CM
CM
CM
CM
V
V
− V
− V
+ V
+ V
FIGURE 2. Expected Input Signal Range
IN +
CM
Signals Will Reduce the Output Level
REF
REF
REF
REF
REF
E
, and be centered around a V
FS
/2
/4
/2
/2
IN
+ and V
= 4096 ( 1 - sin (90˚ + dev))
V
V
V
V
CM
CM
CM
CM
IN
Input
− should EACH not exceed the
V
+ V
+ V
V
− V
− V
CM
IN −
REF
REF
REF
RE/2F
CM
/2
/4
/4
. The peak-to-peak volt-
20014812
20014811
0000 0000 0000
0100 0000 0000
1000 0000 0000
1100 0000 0000
1111 1111 1111
CM
Output
.
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