ADA4530-1ARZ-R7 datasheet(30/51 Pages) AD

30 / 51 page

Data Sheet

ADA4530-1

Rev. A | Page 29 of 50

GAIN STAGE

The second stage of the amplifier comprises an NMOS differen-

tial pair (M3, M4) and folded cascode transistors (M13 to M20).

The amplifier features nested Miller compensation (C1 to C3).

OUTPUT STAGE

The ADA4530-1 features a complementary common-source

output stage consisting of the M21 and M22 transistors. These

transistors are configured in a Class AB topology and are biased

by the voltage source, V1. This topology allows the output

voltage to be within tens of millivolts of the supply rails,

achieving a rail-to-rail output swing. The output voltage is

limited by the output impedance of the transistors. The output

voltage swing is a function of the load current and can be

estimated using the output voltage to the supply rail vs. load

current graphs (see Figure 40 to Figure 45).

GUARD BUFFER

The guard buffer (BUF1) is a unity-gain amplifier that creates a

low impedance replica of the input common-mode voltage. The

buffer input is connected to the noninverting input (IN+). The

noninverting input voltage is approximately equal to the input

common-mode voltage when the main amplifier feedback loop

is settled.

The guard buffer uses a three-stage architecture similar to that

of the amplifier. The guard buffer uses a rail-to-rail output stage

that allows the guard voltage to swing within 100 mV of the

supply rails. Because the guard buffer output follows the input

common-mode voltage, this output swing limits the effectiveness

of the guard buffer at low input common-mode voltages. This

limit can be seen as a significant increase in input bias current

at low common-mode voltages in the input bias current vs.

common-mode voltage graphs (see Figure 22 to Figure 33). For

this reason, it is not recommended to operate the circuit with an

input common-mode voltage of less than 100 mV from the V−

supply rail.

The guard buffer output voltage can be degraded from excessive

loading. The 1 kΩ output resistance adds 1 μV of guard voltage

error per 1 nA of load current. It is possible to drive the guard

offset voltage out of its specifications with a few tens of nano-

amperes of load current. For this reason, it is not recommended

to drive anything except insulation resistance (see the Insulation

Resistance and Guarding section) with the guard buffer. If more

drive strength is needed, the guard voltage can be buffered with

a low offset, low input bias current op amp such as the

ADA4661-2.

ADA4530-1ARZ-R7 数据表(PDF) 30 Page - Analog Devices

ADA4530-1ARZ-R7 数据表(HTML) 30 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

数据表下载