Design & Operating Notes:
1. The ALD1706A/ALD1706B/ALD1706/ALD1706G 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
ALD1706A/ALD1706B/ALD1706/ALD1706G 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 ALD1706A/ALD1706B/ALD1706/ALD1706G 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 ALD1706A/ALD1706B/ALD1706/ALD1706G
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 ALD1706A/ALD1706B/ALD1706/ALD1706G 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 ALD1706A/ALD1706B/ALD1706/ALD1706G , 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 less than 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
80
-25°C
60
40
20
0
0
±1
+70°C
±2
±3
±4
SUPPLY VOLTAGE (V)
+125°C
±5
±6
T
A
= -55°C
±7
COMMON MODE INPUT
VOLTAGE RANGE (V)
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
SUPPLY VOLTAGE (V)
T
A
= 25°C
SUPPLY CURRENT (µA)
+25°C
OPEN LOOP VOLTAGE GAIN AS AFUNCTION
OF LOAD RESISTANCE
1000
10000
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
INPUT BIAS CURRENT (pA)
OPEN LOOP VOLTAGE
GAIN (V/mV)
1000
100
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)
ALD1706A/ALD1706B
ALD1706/ALD1706G
Advanced Linear Devices
4 of 9
ALD [ ADVANCED LINEAR DEVICES ]
