Design & Operating Notes:
temperature. This low input bias current assures that the analog signal
from the source will not be distorted by input bias currents. Normally,
this extremely high input impedance of greater than 1012Ω would not
be a problem as the source impedance would limit the node impedance.
However, for applications where source impedance is very high, it may
be necessary to limit noise and hum pickup through proper shielding.
1. TheALD2701A/ALD2701B/ALD2701 CMOS operational amplifier uses
a 3 gain stage architecture and an improved frequency compensation
scheme to achieve large voltage gain, high output driving capability,
and better frequency stability. In a conventional CMOS operational
amplifier design, compensation is achieved with a pole splitting
capacitor together with a nulling resistor. This method is, however,
very bias dependent and thus cannot accommodate the large range
of supply voltage operation as is required from a stand alone CMOS
operational amplifier. TheALD2701A/ALD2701B/ALD2701 is internally
compensated for unity gain stability using a novel scheme that does
not use a nulling resistor. This scheme produces a clean single pole
roll off in the gain characteristics while providing for more than 70
degrees of phase margin at the unity gain frequency.
4. The output stage consists of class AB complementary output drivers,
capable of driving a low resistance load. The output voltage swing is
limited by the drain to source on-resistance of the output transistors as
determined by the bias circuitry, and the value of the load resistor.
When connected in the voltage follower configuration, the oscillation
resistant feature, combined with the rail to rail input and output feature,
makes an effective analog signal buffer for medium to high source
impedance sensors, transducers, and other circuit networks.
2. The ALD2701A/ALD2701B/ALD2701 has complementary p-channel
and n-channel input differential stages connected in parallel to
accomplish rail to rail input common mode voltage range. This means
that with the ranges of common mode input voltage close to the power
supplies, one of the two differential stages is switched off internally.
To maintain compatibility with other operational amplifiers, this switching
point has been selected to be about 1.5V below the positive supply
voltage. Since offset voltage trimming on the ALD2701A/ALD2701B/
ALD2701 is made when the input voltage is symmetrical to the supply
voltages, this internal switching does not affect a large variety of
applications such as an inverting amplifier or non-inverting amplifier
with a gain larger than 2.5 (5V operation), where the common mode
voltage does not make excursions above this switching point. The
user should however, be aware that this switching does take place if
the operational amplifier is connected as a unity gain buffer, and should
make provision in his design to allow for input offset voltage variations.
5. The ALD2701A/ALD2701B/ALD2701 operational amplifier has been
designed to provide full static discharge protection. Internally, the
design has been carefully implemented to minimize latch up. However,
care must be exercised when handling the device to avoid strong static
fields that may degrade a diode junction, causing increased input
leakage currents. In using the operational amplifier, the user is advised
to power up the circuit before, or simultaneously with, any input voltages
applied and to limit input voltages not to exceed 0.3V of the power
supply voltage levels.
6. The ALD2701A/ALD2701B/ALD2701, with its micropower operation,
offers numerous benefits in reduced power supply requirements, less
noise coupling and current spikes, less thermally induced drift, better
overall reliability due to lower self heating, and lower input bias current.
It requires practically no warm up time as the chip junction heats up to
only 0.2°C above ambient temperature under most operating
conditions.
3. The input bias and offset currents are essentially input protection diode
reverse bias leakage currents, and are typically less than 1pA at room
TYPICAL PERFORMANCE CHARACTERISTICS
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
±7
±6
INPUTS GROUNDED
+25°C
OUTPUT UNLOADED
800
600
400
200
0
T
= 25°C
A
±5
±4
-25°C
T
A
= -55°C
±3
±2
±1
0
+125°C
±5
+70°C
0
±1
±2
±3
±4
±5
±6
±7
0
±1
±2
±3
±4
±6
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
OPEN LOOP VOLTAGE GAIN AS A
FUNCTION OF LOAD RESISTANCE
1000
100
10
10000
1000
V
= ±2.5V
S
100
10
1.0
0.1
V
T
= ±2.5V
= 25°C
S
A
1
10K
100K
1M
10M
-50 -25
0
25
50
75
100
125
LOAD RESISTANCE (Ω)
AMBIENT TEMPERATURE (°C)
ALD2701A/ALD2701B
ALD2701
Advanced Linear Devices
4 of 9
ALD [ ADVANCED LINEAR DEVICES ]
