PCMD3140 datasheet(32/111 Pages) TI

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7.3.6.6 Programmable Channel Summer and Digital Mixer

For applications that require an even higher SNR than that supported for each channel, the device digital

summing mode can be used. In this mode, the digital record data are summed up across the channel with an

equal weightage factor, which helps in reducing the effective record noise. Table 7-17 lists the configuration

settings available for channel summing mode.

Table 7-17. Channel Summing Mode Programmable Settings

P0_R107_D[3:2] : CH_SUM[2:0]

CHANNEL SUMMING MODE FOR INPUT CHANNELS

SNR AND DYNAMIC RANGE

BOOST

00 (default)

Channel summing mode is disabled

Not applicable

Output channel 1 = (input channel 1 + input channel 2) / 2

3-dB boost in SNR and dynamic

range

Output channel 2 = (input channel 1 + input channel 2) / 2

Output channel 3 = (input channel 3 + input channel 4) / 2

3-dB boost in SNR and dynamic

range

Output channel 4 = (input channel 3 + input channel 4) / 2

Reserved (do not use this setting)

Not applicable

Reserved (do not use this setting)

Not applicable

The device additionally supports a fully programmable mixer feature that can mix the various input channels

with their custom programmable scale factor to generate the final output channels. The programmable mixer

feature is available only if CH_SUM[2:0] is set to 2'b00. The mixer function is supported for all 4 input

channels. Figure 7-18 shows a block diagram that describes the mixer 1 operation to generate output channel

1. The programmable coefficients for the mixer operation are located in the Section 7.6.3.3 section. All mixer

coefficients are 32-bit, two’s complement numbers using a 1.31 number format. The value of 0x7FFFFFFF is

equivalent to +1 (0-dB gain), the value 0x00000000 is equivalent to mute (zero data), and any values in between

set the mixer attenuation computed using Equation 3. If the MSB is set to '1' then the attenuation remains the

same but the signal phase is inverted.

hex2dec (value) / 231

(3)

Input Channel-1

Processed Data

Input Channel-2

Processed Data

Input Channel-3

Processed Data

Input Channel-4

Processed Data

Attenuated by

MIX1_CH1

factor

Attenuated by

MIX1_CH2

factor

Attenuated by

MIX1_CH3

factor

Attenuated by

MIX1_CH4

factor

Output Channel-1

Routed to Bi-Quad

Filter

Figure 7-18. Programmable Digital Mixer Block Diagram

A similar mixer operation is performed by mixer 2, mixer 3, and mixer 4 to generate output channel 2, channel 3,

and channel 4, respectively.

PCMD3140-Q1

SBASAH3A – APRIL 2022 – REVISED SEPTEMBER 2022

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