STA323W datasheet(61/71 Pages) STMICROELECTRONICS

61 / 71 page

STA323W

User-programmable settings

61/71

8.5

Calculating 24-bit signed fractional numbers from a dB value

The pre-scale, mixing, and post-scale functions of the STA323W use 24-bit signed fractional

multipliers to attenuate signals. These attenuations can also invert the phase and therefore

range in value from -1 to +1.

It is possible to calculate the coefficient to use for a given negative dB value (attenuation)

using the equations following.

●

non-inverting phase numbers 0 to +1:

–

coefficient = round(8388607 * 10 ^ (dB/20))

●

inverting phase numbers 0 to -1:

–

coefficient = 16777216 - round(8388607 * 10^(dB/20))

As can be seen by the preceding equations, the value for positive phase 0dB is 0x7FFFFF

and the value for negative phase 0dB is 0x800000.

8.6

User defined coefficient RAM

8.6.1

Coefficient address register 1 (address 0x16)

8.6.2

Coefficient b1data register bits 23...16 (address 0x17)

8.6.3

Coefficient b1data register bits 15...8 (address 0x18)

8.6.4

Coefficient b1data register bits 7...0 (address 0x19)

CFA7

CFA6

CFA5

CFA4

CFA3

CFA2

CFA1

CFA0

000000

C1B23

C1B22

C1B21

C1B20

C1B19

C1B18

C1B17

C1B16

000

C1B15

C1B14

C1B13

C1B12

C1B11

C1B10

C1B9

C1B8

0000

C1B7

C1B6

C1B5

C1B4

C1B3

C1B2

C1B1

C1B0

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