8.2.2.3 Noise Performance

The autocalibration technique used by the INA333-Q1 results in reduced low frequency noise, typically only

50 nV/√Hz (G = 100). The spectral noise density is shown in detail in Figure 6-8. The low-frequency noise of the

device is approximately 1 μVPP measured from 0.1 Hz to 10 Hz (G = 100).

8.2.2.4 Input Bias Current Return Path

The input impedance of the INA333-Q1 is extremely high; approximately 100 GΩ. However, a path must

be provided for the input bias current of both inputs. This input bias current is typically ±70 pA. High input

impedance means that this input bias current changes very little with varying input voltage.

Input circuitry must provide a path for this input bias current for proper operation. Figure 8-3 shows various

provisions for an input bias current path. Without a bias current path, the inputs float to a potential that exceeds

the common-mode range of the device, and the input amplifiers saturate. If the differential source resistance is

low, the bias current return path can be connected to one input (see the thermocouple example in Figure 8-3).

With higher source impedance, use two equal resistors to provide a balanced input with the possible advantages

of a lower input offset voltage as a result of bias current, and improved high-frequency common-mode rejection.

GND

INA333-Q1

±

+

INA333-Q1

±

+

Thermocouple

10 NŸ

INA333-Q1

±

+

Microphone,

Hydrophone,

and more

Figure 8-3. Providing an Input Common-Mode Current Path

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INA333-Q1

SBOS464B – SEPTEMBER 2019 – REVISED JUNE 2023

Copyright © 2023 Texas Instruments Incorporated

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Product Folder Links: INA333-Q1