Silicon Laboratories SI2494/39 Speakerphone Calibration-AEC Gain Calibration, Reg Name Bit U19E

AN93

7.7.3.3. Speakerphone Calibration—AEC Gain Calibration

Figure 36 illustrates the setup used to set AEC speaker reference gain (U19C) and the AEC microphone input signal gain (U19D). Here the modem has the AEC/AES enabled (AT+VSP=1) with the calibrated UB1 and UB5 values, which where obtained from the two previous sections. Using the Si24xx-VMB, call the remote phone and establish a voice call. Use the command sequence in Table 135.

The AECREF (U19E) contains the energy information of both the AEC speaker reference signal (SPKREF) and the microphone signal (MICREF). The SPKREF bits represent the AEC speaker reference energy, and MICREF bits represent the AEC microphone input energy. The energy value is computed from average(s[t]^2).

Reg.	Name	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit	Bit
		15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
U19E	AECREF				SPKREF								MICREF

Send the white noise from the remote phone so that the energy level at the meter (Tip and Ring) is -15dBm. Use the AT:R19E command to read the contents of the U19E register. Adjust the AEC gain (U19C) of the speaker reference signal until SPKREF reaches a value as close to 0x38 as possible. Adjust the AEC gain (U19D) of the microphone input signal until MICREF has a value as close as possible to 0x38.

U19C and U19D are calibrated when the AT:R19E reading is close to 0x3838, with a power-level difference of less than 2dB. Record these values and use them in the initialization sequence defined in Table 119, “Initialization Sequence,” on page 194.

Figure 36. AEC Gain Calibration

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