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參數資料
| 型號： | AD9020JZ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | 10-Bit 60 MSPS A/D Converter |
| 中文描述： | 1-CH 10-BIT FLASH METHOD ADC, PARALLEL ACCESS, CQFP68 |
| 封裝： | CERAMIC, LCC-68 |
| 文件頁數： | 8/12頁 |
| 文件大?。?/td> | 204K |
| 代理商： | AD9020JZ |
AD9020
–8–
REV. A
USING T HE AD9020
Voltage References
T he AD9020 requires that the user provide two voltage refer-
ences: +V
REF
and –V
REF
. T hese two voltages are applied across
an internal resistor ladder (nominally 37
) and set the analog
input voltage range of the converter. T he voltage references
should be driven from a stable, low impedance source. In addi-
tion to these two references, three evenly spaced taps on the re-
sistor ladder (1/4
REF
, 1/2
REF
, 3/4
REF
) are available. Providing a
reference to these quarter points on the resistor ladder will im-
prove the integral linearity of the converter and improve ac per-
formance. (AC and dc specifications are tested while driving the
quarter points at the indicated levels.) T he figure below is not
intended to show the transfer function of the ADC, but illus-
trates how the linearity of the device is affected by reference
voltages applied to the ladder.
Effect of Reference Taps on Linearity
Resistance between the reference connections and the taps of
the first and last comparators causes offset errors. T hese errors,
called “top and bottom of the ladder offsets,” can be nulled by
using the voltage sense lines, +V
SENSE
and –V
SENSE
, to adjust the
reference voltages. Current through the sense lines should be
limited to less than 100
μ
A. Excessive current drawn through
the voltage sense lines will affect the accuracy of the sense line
voltage.
T he next page shows a reference circuit which nulls out the off-
set errors using two op amps and provides appropriate voltage
references to the quarter-point taps. Feedback from the sense
lines causes the op amps to compensate for the offset errors.
T he two transistors limit the amount of current drawn directly
from the op amps; resistors at the base connections stabilize
their operation. T he 10 k
resistors (R1–R4) between the volt-
age sense lines form an external resistor ladder; the quarter
point voltages are taken off this external ladder and buffered by
an op amp. T he actual values of resistors R1–R4 are not critical,
but they should match well and be large enough (
≥
10 k
) to
limit the amount of current drawn from the voltage sense lines.
T he select resistors (R
S
) shown in the schematic (each pair can
be a potentiometer) are chosen to adjust the quarter-point volt-
age references, but are not necessary if R1–R4 match within
0.05%.
An alternative approach for defining the quarter-point refer-
ences of the resistor ladder is to evaluate the integral linearity
error of an individual device, and adjust the voltage at the
quarter-points to minimize this error. T his may improve the low
frequency ac performance of the converter.
Performance of the AD9020 has been optimized with an analog
input voltage of
±
1.75 V (as measured at
±
V
SENSE
). If the ana-
log input range is reduced below these values, relatively larger
differential nonlinearity errors may result because of comparator
mismatches. As shown in the figure below, performance of the
converter is a function of
±
V
SENSE
.
E
S
32
38
44
50
56
62
10.0
9.0
8.0
7.0
6.0
5.0
0.4
0.8
1.0
±V
SENSE
– Volts
1.4
1.8
2.0
0.6
1.2
1.6
AD9020 SNR and ENOB vs. Reference Voltage
Applying a voltage greater than 4 V across the internal resistor
ladder will cause current densities to exceed rated values, and
may cause permanent damage to the AD9020. T he design of
the reference circuit should limit the voltage available to the
references.
Analog Input Signal
T he signal applied to ANALOG IN drives the inputs of 512
parallel comparator cells (see Equivalent Analog Input figure).
T his connection typically has an input resistance of 7 k
, and
input capacitance of 45 pF. T he input capacitance is nearly
constant over the analog input voltage range, as shown in the
graph which illustrates that characteristic.
T he analog input signal should be driven from a low distortion,
low noise amplifier. A good choice is the AD9617, a wide band-
width, monolithic operational amplifier with excellent ac and dc
performance. T he input capacitance should be isolated by a
small series resistor (24
for the AD9617) to improve the ac
performance of the amplifier (see AD9020/PCB Evaluation
Board Block Diagram).
相關PDF資料 |
PDF描述 |
|---|---|
| AD9020KE | CONNECTOR |
| AD9020KZ | 10-Bit 60 MSPS A/D Converter |
| AD9020PCB | 10-Bit 60 MSPS A/D Converter |
| AD9034 | 12-Bit 20 MSPS A/D Converter(20MSPS 12位A/D轉換器) |
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9020KE | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| AD9020KJ | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| AD9020KZ | 制造商:Rochester Electronics LLC 功能描述:10 BIT 60 MSPS TTL ADC - Bulk |
| AD9020PCB | 制造商:AD 制造商全稱:Analog Devices 功能描述:10-Bit 60 MSPS A/D Converter |
| AD9020SE/883 | 制造商:AD 制造商全稱:Analog Devices 功能描述:10-Bit 60 MSPS A/D Converter |
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