LM4675 PA to create human voice using PWM signal

HENG MA

Other Parts Discussed in Thread: LM4675, CC3200

Hi All

I am trying to use LM4675 PA to create human voice. I got the following questions:

1. In this case, I want to use single ended input mode, which IN- is connected to the signal input while IN+ is connected to GND through a serial RC components. Can I use a PWM signal generated from MCU such as CC3200 to retrieve the human voice? The illustration of problem is plotted below.

2. There are two outputs of LM4675 which are Vo1 and Vo2. Should Vo1 be connected to the "+" of 8 ohm speaker and Vo2 connected to the "-" of 8 ohm speaker? Or polarity of speaker does not matter?

Thanks

Heng

over 9 years ago

0 Andy Liu (BMS) over 9 years ago

TI__Guru 52115 points

I will take a look at you question and get back to you soon.

0 Andy Liu (BMS) over 9 years ago in reply to Andy Liu (BMS)

TI__Guru 52115 points

Hi Heng,

See my comments below:

a) The PWM signal cannot be directly used as the input of the LM4675. First you have to convert the PWM to a pure analog signal, which could be done with a LPF. I would suggest you try a 2nd order LPF.

b) Vo2 is out of phase again the input phase while Vo1 is in phase. In case of mono, you don'n have to care about the the polarity of speaker. However, in case of stereo, the speaker polarity does matter. If the connections are wrong, the sound will be strange.

Andy

0 HENG MA over 9 years ago in reply to Andy Liu (BMS)

Expert 1020 points

Hi Andy

Thanks for your reply.

Heng

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LM4675 PA to create human voice using PWM signal