Design & Operating Notes:
1. The ALD1702/ALD1703 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 ALD1702 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.
A unity gain buffer using the ALD1702 will typically drive 400pF of
external load capacitance without stability problems. In the inverting
unity gain configuration, it can drive up to 800pF of load capacitance.
Compared to other CMOS operational amplifiers, the ALD1702
has shown itself to be more resistant to parasitic oscillations.
2. The ALD1702/ALD1703 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 compa-
tibility with other operational amplifiers, this switching point has been
selected to be about 1.5V above the negative supply voltage. Since
offset voltage trimming on the ALD1702/ALD1703 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 below 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 ALD1702/ALD1703 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.
TYPICAL PERFORMANCE CHARACTERISTICS
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
±7
OPEN LOOP VOLTAGE GAIN AS A FUNCTION
OF SUPPLY VOLTAGE AND TEMPERATURE
1000
COMMON MODE INPUT
VOLTAGE RANGE (V)
±5
±4
±3
±2
±1
0
0
±1
±2
±3
±4
±5
±6
±7
OPEN LOOP VOLTAGE
GAIN (V/mV)
±6
T
A
= 25°C
}
-55°C
}
+25°C
100
}
+125°C
10
R
L
= 10KΩ
R
L
= 5KΩ
1
0
±2
±4
SUPPLY VOLTAGE (V)
±6
±8
SUPPLY VOLTAGE (V)
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
10000
±5
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
INPUTS GROUNDED
OUTPUT UNLOADED
INPUT BIAS CURRENT (pA)
1000
100
SUPPLY CURRENT (mA)
V
S
=
±
2.5V
±4
±3
±2
±1
0
T
A
= -55ºC
-25°C
+25°C
+80°C
+125°C
10
1.0
0.1
-50
-25
0
25
50
75
100
125
0
±1
±2
±3
±4
±5
±6
AMBIENT TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
ALD1702A/ALD1702B
ALD1702/ALD1703
Advanced Linear Devices
4
ALD [ ADVANCED LINEAR DEVICES ]
