ALD1706A/ALD1706B

Advanced Linear Devices

4

ALD1706/ALD1706G

Design & Operating Notes:

1. The ALD1706 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 ALD1706 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 ALD1706 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

ALD1706 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

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 ALD1706 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 ALD1706, 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

INPUT BIAS CURRENT AS A FUNCTION

OF AMBIENT TEMPERATURE

AMBIENT TEMPERATURE (

°C)

1000

100

10

0.1

1.0

100

-25

0

75

125

50

25

-50

10000

OPEN LOOP VOLTAGE GAIN AS AFUNCTION

OF LOAD RESISTANCE

10M

LOAD RESISTANCE (

Ω)

10K

100K

1M

1000

100

10

1

SUPPLY CURRENT AS A FUNCTION

OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

100

80

40

60

0

20

0

±1

±2

±3

±4

±5

±6

-25

°C +25°C

+70

°C

+125

°C

INPUTS GROUNDED

OUTPUT UNLOADED

COMMON MODE INPUT VOLTAGE RANGE

AS A FUNCTION OF SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

±7

±6

±5

±4

±3

±2

±1

0

0

±1

±2

±3

±4

±5

±6

±7