Design & Operating Notes:
1. The ALD1701A/ALD1701B/ALD1701/ALD1701G 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 ALD1701A/ALD1701B/
ALD1701/ALD1701G 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 characteris-
tics while providing for more than 70 degrees of phase margin at the
unity gain frequency.
2. The ALD1701A/ALD1701B/ALD1701/ALD1701G has complemen-
tary 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 ampli-
fiers, this switching point has been selected to be about 1.5V below
the positive supply voltage. Since offset voltage trimming on the
ALD1701A/ALD1701B/ALD1701/ALD1701G 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 excur-
sions 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 ALD1701A/ALD1701B/ALD1701/ALD1701G operational ampli-
fier 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 ALD1701A/ALD1701B/ALD1701/ALD1701G, 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
±7
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
±6
±5
±4
±3
±2
±1
0
T
A
= 25°C
+25°C
-25°C
COMMON MODE INPUT
VOLTAGE RANGE (V)
SUPPLY CURRENT (µA)
400
300
T
A
= -55°C
200
100
0
0
±1
±2
±3
±4
±5
±6
SUPPLY VOLTAGE (V)
+125°C
+70°C
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
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)
ALD1701A/ALD1701B
ALD1701/ALD1701G
Advanced Linear Devices
4 of 9
ALD [ ADVANCED LINEAR DEVICES ]
