Design & Operating Notes:
1. The 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 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 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
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 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 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
T
A
= -55°C
120
80
40
+70°C
0
0
±1
±2
±3
±4
±5
±6
SUPPLY VOLTAGE (V)
+125°C
+25°C
±7
±6
T
A
= 25°C
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
SUPPLY CURRENT (µA)
COMMON MODE INPUT
VOLTAGE RANGE (V)
-25°C
±5
±4
±3
±2
±1
0
0
±1
±2
±3
±4
±5
±6
±7
SUPPLY VOLTAGE (V)
OPEN LOOP VOLTAGE GAIN AS A
FUNCTION OF LOAD RESISTANCE
1000
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
10000
INPUT BIAS CURRENT (pA)
1000
100
V
S
=
±2.5V
OPEN LOOP VOLTAGE
GAIN (V/mV)
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
ALD [ ADVANCED LINEAR DEVICES ]
