Design & Operating Notes:
1. The ALD1704 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. The ALD1704 is internally compensated for unity
gain stability using a novel scheme that 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 ALD1704 will typically drive 400pF of external load
capacitance without stability problems. In the inverting unity gain
configuration, itcandriveupto800pFofloadcapacitance. Compared
to other CMOS operational amplifiers, the ALD1704 has shown itself
to be more resistant to parasitic oscillations.
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. For applica-
tions 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 symmetrical class AB complementary
output drivers, capable of driving a low resistance load with up to 10mA
source current and 10mA sink current. The output voltage swing is
limited by the drain to source on-resistance of the output transistors as
determinedbythebiascircuitry, andthevalueoftheloadresistor. When
connected in the voltage follower configuration, the oscillation resistant
feature, combined with the rail-to-rail input and output feature, makes
theALD1704aneffectiveanalogsignalbufferformediumtohighsource
impedance sensors, transducers, and other circuit networks.
2. The ALD1704 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 compat-
ibility 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 ALD1704 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 (10V
operation), where the common mode voltage does not make excur-
sions below this switching point.
5. The ALD1704 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
OPEN LOOP VOLTAGE GAIN AS A FUNCTION
OF SUPPLY VOLTAGE AND TEMPERATURE
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
1000
±7
T
= 25°C
A
} -55°C
} +25°C
±6
100
±5
±4
±3
} +125°C
10
1
R = 10KΩ
L
R = 5KΩ
L
±2
±3
±5
SUPPLY VOLTAGE (V)
±2
±4
±6
±7
0
±2
±4
±6
±8
SUPPLY VOLTAGE (V)
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
5
4
10000
1000
INPUTS GROUNDED
OUTPUT UNLOADED
V
S
= ±5.0V
100
10
3
T
= -55°C
A
2
1
-25°C
+25°C
+80°C
1.0
0.1
+125°C
0
0
±1
±2
±3
±4
±5
±6
-50 -25
0
25
50
75
100
125
AMBIENT TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
ALD1704A/ALD1704B
ALD1704/ALD1704G
Advanced Linear Devices
4
ALD [ ADVANCED LINEAR DEVICES ]
