Design & Operating Notes:
1. The ALD4706 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
voltageoperationasisrequiredfromastandaloneCMOSoperational
amplifier. The ALD4706 is internally compensated for unity gain
stabilityusinganovelschemethatdoesnotuseanullingresistor. 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.
roomtemperature. Thislowinputbiascurrentassuresthattheanalog
signal from the source will not be distorted by input bias currents.
Normally, this extremely high input impedance of greater than 1013Ω
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.
2. The ALD4706 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
compatibilitywithotheroperationalamplifiers, thisswitchingpointhas
been selected to be about 1.5V below the positive supply voltage.
Sinceoffsetvoltagetrimmingonthe ALD4706ismadewhentheinput
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),wherethecommonmodevoltagedoesnotmakeexcursions
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.
5. The ALD4706 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 ALD4706, with its ultra micropower operation, offers numerous
benefits in reduced power supply requirements, less noise coupling
and current spikes, less thermally induced drift, better overall reli-
ability 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.
3. Theinputbiasandoffsetcurrentsareessentiallyinputprotectiondiode
reverse bias leakage currents, and are typically less than 0.1pA at
TYPICAL PERFORMANCE CHARACTERISTICS
OPEN LOOP VOLTAGE GAIN AS A
FUNCTION OF LOAD RESISTANCE
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
1000
100
10
INPUTS GROUNDED
OUTPUT UNLOADED
+25°C
-25°C
320
240
160
80
T
= -55°C
A
V
T
= ±2.5V
= 25°C
S
A
+70°C +125°C
1
0
10K
100K
1M
10M
0
±1
±2
±3
±4
±5
±6
LOAD RESISTANCE (Ω)
SUPPLY VOLTAGE (V)
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
±7
±6
10000
1000
T
= 25°C
A
V
= ±2.5V
S
±5
±4
100
10
±3
±2
±1
0
1.0
0.1
0
±1
±2
±3
±4
±5
±6
±7
-50 -25
0
25
50
75
100
125
AMBIENT TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
ALD4706A/ALD4706B
ALD4706
Advanced Linear Devices
4
ALD [ ADVANCED LINEAR DEVICES ]
