OP1177/OP2177/OP4177

Data Sheet

Rev. I | Page 14 of 24

FUNCTIONAL DESCRIPTION

The OPx177 series is the fourth generation of Analog Devices,

Inc., industry-standard OP07 amplifier family. OPx177 is a

high precision, low noise operational amplifier with a

combination of extremely low offset voltage and very low input

bias currents. Unlike JFET amplifiers, the low bias and offset

currents are relatively insensitive to ambient temperatures,

even up to 125°C.

Analog Devices proprietary process technology and linear design

expertise has produced a high voltage amplifier with superior

performance to the OP07, OP77, and OP177 in a tiny MSOP

8­lead package. Despite its small size, the OPx177 offers numerous

improvements, including low wideband noise, very wide input

and output voltage range, lower input bias current, and

complete freedom from phase inversion.

OPx177 has a specified operating temperature range as wide as

any similar device in a plastic surface-mount package. This is

increasingly important as PCB and overall system sizes continue

to shrink, causing internal system temperatures to rise. Power

consumption is reduced by a factor of four from the OP177,

and bandwidth and slew rate increase by a factor of two. The

low power dissipation and very stable performance vs.

temperature also act to reduce warmup drift errors to

insignificant levels.

Open-loop gain linearity under heavy loads is superior to compet-

itive parts, such as the OPA277, improving dc accuracy and

reducing distortion in circuits with high closed-loop gains.

Inputs are internally protected from overvoltage conditions

referenced to either supply rail.

Like any high performance amplifier, maximum performance is

achieved by following appropriate circuit and PCB guidelines.

The following sections provide practical advice on getting the

most out of the OPx177 under a variety of application conditions.

TOTAL NOISE-INCLUDING SOURCE RESISTORS

The low input current noise and input bias current of the OPx177

make it useful for circuits with substantial input source resistance.

Input offset voltage increases by less than 1 μV maximum per

500 Ω of source resistance.

The total noise density of the OPx177 is



S

S

n

n

TOTAL

n

kTR

R

i

e

e

4

2

2

,







where:

en is the input voltage noise density.

in is the input current noise density.

RS is the source resistance at the noninverting terminal.

k is Boltzmann’s constant (1.38 × 10−23 J/K).

T is the ambient temperature in Kelvin (T = 273 + temperature

in degrees Celsius).

For RS < 3.9 kΩ, en dominates and

en,TOTAL ≈ en

For 3.9 kΩ < RS < 412 kΩ, voltage noise of the amplifier, the

current noise of the amplifier translated through the source

resistor, and the thermal noise from the source resistor all

contribute to the total noise.

For RS > 412 kΩ, the current noise dominates and

en,TOTAL ≈ inRS

The total equivalent rms noise over a specific bandwidth is

expressed as



 BW

e

e

TOTAL

n

n

,



where BW is the bandwidth in hertz.

The preceding analysis is valid for frequencies larger than 50 Hz.

When considering lower frequencies, flicker noise (also known as

1/f noise) must be taken into account.

For a reference on noise calculations, refer to the Band-Pass

KRC or Sallen-Key Filter section.

GAIN LINEARITY

Gain linearity reduces errors in closed-loop configurations. The

straighter the gain curve, the lower the maximum error over the

input signal range. This is especially true for circuits with high

closed-loop gains.

The OP1177 has excellent gain linearity even with heavy loads,

as shown in Figure 51. Compare its performance to the OPA277,

shown in Figure 52. Both devices are measured under identical

conditions, with RL = 2 kΩ. The OP2177 (dual) has virtually no

distortion at lower voltages. Compared to the OPA277 at

several supply voltages and various loads, OP1177 performance

far exceeds that of its counterpart.

(5V/DIV)

OP1177

VSY = ±15V

RL = 2kΩ

Figure 51. Gain Linearity