ST-PLC-AFE datasheet(13/58 Pages) STMICROELECTRONICS

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ST-PLC-AFE

General description

Single to differential gain through the filter is equal to 1. If the single-ended input voltage

amplitude is 1 Vpp, then the output voltage in differential mode is also equal to 1 Vpp.

Figure 8 shows the single-ended to differential gain conversion.

Figure 8. PGA filter connection

2.3

Rx block

The Rx block consists of:

•

Two programmable gain amplifiers (Rx PGA1 and Rx PGA2)

•

A fourth-order, low-pass filter

•

A selectable high-pass filter

The input sensing mode can be differential mode for better noise immunity or single mode

for the lowest BOM.

The Rx PGA1 can be configured through the SPI to operate as either an attenuator or an

amplifier. The gain steps of the Rx PGA1 are -3 dB, 3 dB, 9dB, and 15 dB. The gain can be

programmed through the RX_PGA1<1:0> bits in the Gain register. Configuring the Rx PGA1

as an attenuator (at gains less than 0 dB) is useful for applications where large interference

signals are present within the signal band. Attenuating large interference allows these

signals to pass through the analog Rx signal chain without causing an overload; the

interference signal can then be processed and removed within the microprocessor as

necessary. The gain steps of the Rx PGA2 are -6 dB, 6 dB, 18 dB, and 30 dB. The gain can

be programmed through the RX_PGA2<1:0> bits in the Gain register.

The Rx filter is a very low-noise, unity-gain, fourth-order low-pass filter. Its cutoff frequency

is selectable between CENELEC A or CENELEC B, C, or D bands. The selection of the

band is achieved through the BAND_SEL bit in the Enable register.

The 35 kHz high-pass filter is activated by the HP_EN bit in the Enable register.

Recommended connections for the Rx signal chain are shown in Figure 9, Figure 10, and

Figure 11.

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