ADA4530-1ARZ-R7 datasheet(42/51 Pages) AD

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Data Sheet

ADA4530-1

Rev. A | Page 41 of 50

100

0.01

0.1

0.001

100k

10k

100

0.1

0.01

FREQUENCY (Hz)

VSY = 10V

AV = +1

1TΩ

100GΩ

10GΩ

1GΩ

100MΩ

Figure 118. Current Noise Spectral Density

The current noise of the ADA4530-1 originates from the

saturation current of the ESD diodes. The diode saturation

current has an exponential dependence on temperature;

therefore, it is expected that the current noise tracks this

temperature behavior. The current noise of the ADA4530-1 is

characterized over temperature using the transimpedance

measurement circuit with a 1 TΩ resistor. The measurements

are limited to 85°C because of the maximum operating

temperature of the resistor. Figure 119 shows the current noise

density at a frequency of 0.1 Hz for all of the test temperatures.

It can be useful to calculate an equivalent noise resistance from

the current noise density data in Figure 119. This conversion

facilitates comparisons between the current noise generated by

the ADA4530-1 and the thermal noise of the feedback resistor

used in the circuit.

800

200

400

600

700

100

300

500

090

TEMPERATURE (°C)

VSY = 10V

f = 0.1Hz

Figure 119. Current Noise Density vs. Temperature

Figure 120 shows the equivalent noise resistance vs. temperature.

From Figure 120, it is simple to determine that the ADA4530-1

contributes less noise than a 1 TΩ resistor for temperatures less

than 40°C. If the application requires 85°C operation, the

ADA4530-1 contributes as much noise as a 30 GΩ resistor. This

example illustrates the considerable impact that temperature

plays in determining the noise performance of an application.

10T

10G

100G

090

TEMPERATURE (°C)

f = 0.1Hz

Figure 120. Equivalent Noise Resistance vs. Temperature

In summary, the excellent noise performance of the ADA4530-1

makes it ideal for electrometer applications. For impedances

less than 1 TΩ, the amplifier noise is negligible. Also, unlike

other amplifiers, the current noise has been fully characterized

and is free of excessive blowback noise.

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