Design & Operating Notes:
1. The ALD2706A/ALD2706B/ALD2706 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. The
ALD2706A/ALD2706B/ALD2706 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.
2. The ALD2706A/ALD2706B/ALD2706 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 ALD2706A/ALD2706B/ALD2706 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.
3. The input bias and offset currents are essentially input protection
diode reverse bias leakage currents, and are typically less than
1pA at room 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 10
12
Ω
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.
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.
5. The ALD2706A/ALD2706B/ALD2706 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 to not
exceed 0.3V of the power supply voltage levels.
6. The ALD2706A/ALD2706B/ALD2706, 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 0.1°C above ambient temperature under
most operating conditions.
TYPICAL PERFORMANCE CHARACTERISTICS
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
INPUTS GROUNDED
OUTPUT UNLOADED
160
-25°C
120
80
40
0
0
±1
±2
±3
+70°C
±4
+125°C
±5
±6
T
A
= -55°C
±7
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
±6
±5
±4
±3
±2
±1
0
0
±1
±2
±3
±4
±5
±6
±7
T
A
= 25°C
SUPPLY CURRENT (µA)
SUPPLY VOLTAGE (V)
COMMON MODE INPUT
VOLTAGE RANGE (V)
+25°C
SUPPLY VOLTAGE (V)
OPEN LOOP VOLTAGE GAIN AS AFUNCTION
OF LOAD RESISTANCE
1000
INPUT BIAS CURRENT (pA)
10000
1000
100
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
OPEN LOOP VOLTAGE
GAIN (V/mV)
V
S
=
±2.5V
100
10
10
V
S
=
±2.5V
T
A
= 25°C
1
10K
100K
1M
10M
1.0
0.1
-50
-25
0
25
50
75
100
125
LOAD RESISTANCE (Ω)
AMBIENT TEMPERATURE (°C)
ALD2706A/ALD2706B
ALD2706
Advanced Linear Devices
4 of 9
ALD [ ADVANCED LINEAR DEVICES ]
