10

100

1k

10k

FREQUENCY (Hz)

1

10

100

GAIN = 1000

GAIN = 500

GAIN = 250

GAIN = 100

GAIN = 51

GAIN = 10

1

10

100

1000

CLOSED LOOP GAIN (V/V)

0

4

8

12

16

20

24

VS = 5V

f = 100 Hz

16

LMP2021, LMP2022

SNOSAY9G – SEPTEMBER 2008 – REVISED FEBRUARY 2016

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Product Folder Links: LMP2021 LMP2022

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Copyright © 2008–2016, Texas Instruments Incorporated

Device Functional Modes (continued)

Twisted pair cabling and the active front-end’s common-mode rejection provide immunity against low frequency

noise (i.e. 60 Hz or 50 Hz mains) but are ineffective against RF interference. Figure 46 displays this. Even a few

centimeters of PCB trace and wiring for sensors located close to the amplifier can pick up significant 1 GHz RF.

The integrated EMI filters of LMP202x reduce or eliminate external shielding and filtering requirements, thereby

increasing system robustness. A larger EMIRR means more rejection of the RF interference. For more

information on EMIRR, please refer to AN-1698 (Literature Number SNOA497).

7.4.2 Input Voltage Noise

The input voltage noise density of the LMP202x has no 1/f corner, and its value depends on the feedback

network used. This feature of the LMP202x differentiates this family from other products currently available from

other vendors. In particular, the input voltage noise density decreases as the closed loop voltage gain of the

LMP202x increases. The input voltage noise of the LMP202x is less than 11 nV/

√Hz when the closed loop

voltage gain of the op amp is 1000. Higher voltage gains are required for smaller input signals. When the input

signal is smaller, a lower input voltage noise is quite advantageous and increases the signal to noise ratio.

Figure 35 shows the input voltage noise of the LMP202x as the closed loop gain increases.

Figure 35. Input Voltage Noise Density decreases with Gain

Figure 36 shows the input voltage noise density does not have the 1/f component.

Figure 36. Input Voltage Noise Density with no 1/f

With smaller and smaller input signals and high precision applications with lower error budget, the reduced input

voltage noise and no 1/f noise allow more flexibility in circuit design.