ADA4638-1 查看數據表（PDF） - Analog Devices
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ADA4638-1 Datasheet PDF : 24 Pages
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ADA4638-1
VSY = ±15V
RL = 10kΩ
VIN
Data Sheet
+VSY
A1 ISY+
VOUT
100kΩ
100kΩ
ADA4638-1
VOUT
A2 ISY–
TIME (2µs/DIV)
Figure 58. No Phase Reversal
NOISE CONSIDERATIONS
1/f Noise
1/f noise, also known as pink noise or flicker noise, is inherent
in semiconductor devices and increases as frequency decreases.
At low frequency, 1/f noise is a major noise contributor and
causes a significant output voltage offset when amplified by the
noise gain of the circuit. However, the ADA4638-1 eliminates
the 1/f noise internally, thus making it an excellent choice for dc
or low frequency high precision applications. The 0.1 Hz to
10 Hz voltage noise is only 1.2 μV p-p at ±15 V of supply voltage.
The low frequency 1/f noise appears as a slow varying offset to
the ADA4638-1 and is greatly reduced by the combination of
auto-zeroing and chopping technique. This allows the ADA4638-1
to have a much lower noise at dc and low frequency in comparison
to standard low noise amplifiers that are susceptible to 1/f noise.
Figure 47 and Figure 50 show the voltage noise density of the
ADA4638-1 with no 1/f noise.
COMPARATOR OPERATION
Op amps are designed to operate in a closed-loop configuration
with feedback from its output to its inverting input. Figure 59
shows the ADA4638-1 configured as a voltage follower with an
input voltage, which is kept at midpoint of the power supplies.
A1 and A2 indicate the placement of ammeters to measure supply
currents. ISY+ refers to the current flowing into the positive
supply pin of the op amp, and ISY− refers to the current flowing
out of the negative supply pin of the op amp. From Figure 60, as
expected in normal operating condition, the current flowing
into the op amp is equivalent to the current flowing out of the op
amp, where ISY+ = ISY−.
–VSY
Figure 59. Voltage Follower
1.0
0.8
ISY+
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
ISY–
–1.0
0
5
10
15
20
25
30
VSY (V)
Figure 60. Supply Current vs. Supply Voltage (Voltage Follower)
In contrast to op amps, comparators are designed to work in an
open-loop configuration and to drive logic circuits. Although
op amps are different from comparators, occasionally an unused
section of a dual op amp is used as a comparator to save board
space and cost; however, this is not recommended.
Figure 61 and Figure 62 show the ADA4638-1 configured as
a comparator, with resistors RIN1 and RIN2 in series with the
input pins.
+VSY
A3 ITOTAL+
RIN1
IINPUT+
A1 ISY+
ADA4638-1 VOUT
RIN2
IINPUT–
A2 ISY–
A4 ITOTAL–
–VSY
Figure 61. Comparator A
Rev. 0 | Page 18 of 24
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