ADA4530-1ARZ-R7 datasheet(41/52 Pages) AD

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Data Sheet

ADA4530-1

CURRENT NOISE CONSIDERATIONS

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Rev. C | 41 of 52

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 operat-

ing 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.

Figure 119. Current Noise Density vs. Temperature

Figure 120 shows the equivalent noise resistance vs. temperature.

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

tributes less noise than a 1 TΩ resistor for temperatures less than

40°C. If the application requires an 85°C operation, the ADA4530-1

contributes as much noise as a 30 GΩ resistor. This example illus-

trates the considerable impact of the temperature in determining the

noise performance of an application.

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 is fully characterized and is free of

excessive blowback noise.

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