MX93032 Просмотр технического описания (PDF) - Macronix International

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MX93032

APPLICATION NOTE [M1 VERSION]

Macronix International 

MX93032

DAA CONSIDERATION FOR SPEAKER PHONE

It should be emphasized that DAA circuit plays an important role on improving the performance of speakerphone.This

sub section gives some guides on how the DAA circuit may be "tuned". A diagram of DAA circuit must be given for

simplifying the flowing interpretation.

ACOUSTIC

COUPLING

SPK

DRV

MIC

GAIN

CODEC1

MX93032-M1

CODEC2

LINE

GAIN

LINE

DRV

4 - 2 WIRE

COUPLING

LINE

COUPLING

Referring to figure given above, we have 4 analog amplifiers which are

1.Microphone Pre-Gain (MIC GAIN)

2.Line Out Gain (LINE DRV)

3.Line in Pre-Gain (LINE GAIN)

4.Speaker amplifier (SPK DRV)

Obviously, the 4 amplifiers together with the Line Out volume, Speaker Volume, receive attenuator, transmit attenu-

ator, two volume compensators, acoustical coupling function Hac(f) and line coupling function Hlin(f) compose a

closed loop system. The AEC and LEC will provide additional attenuation to the loop gain one they converge.

To have a better performance on speaker phone, we strongly recommend that analog gain of DAA must satisfy the

following two criteria:

1.As the near end (Microphone side) speaks only, the level at Codec 2 should fulfill that, "codec 2 input must

be less than Codec 2 output due to electrical echo". This meaning can be expressed as

LINE_DRV * Hlin(f) * LINE_GAIN < 1

2.As the far end (Line Side) speaks only, the level at Codec 1 should fulfill that, "Codec 1 output must be

greater than Codec 1 input resulting from acoustical echo". This meaning can be expressed as

SPK_DRV * Hac(f) * MIC_GAIN < 1

By considering the criterion 1, it should pay more attention that minimum echo should be reached by improving the

telephone line interface ( that is, reducing Hlin(f)) and not by reducing LINE_GAIN due to that the MX93032-M1 must

obtain the high enough signal to process. For the same reason for criterion 2, the low echo should be achieved by

good acoustical and mechanical decoupling rather than by decreasing MIC_GAIN.

The ultimate target for hardware design is to create one system which not only satisfies two criteria given above, but

also provides a desirable volume to both speaker and telephone.

P/N:PM0689

REV. 1.0.3, DEC. 13, 1999

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