MP3 chord chip ft1780 with SD/MMC memory card interface

With the rise of MP3 mobile phones, users not only have higher and higher requirements on the volume and sound quality of mobile music, but also have more and more requirements on the storage capacity of mobile phones. They always hope to save more songs and save frequent songs. The troubles. However, the memory that comes with mobile phones is far from meeting these requirements, and many mobile phone platforms cannot support external memory cards. In order to solve this problem, a matching storage management chip is needed.

Fangtai Electronics' ft1780 can help mobile phone design engineers solve this problem well. It not only provides professional MP3 music, but also integrates SD/MMC memory card interface. Thanks to the built-in file management system, it can easily upgrade the original mobile phone products, so that it can replace the external SD/MMC memory card. This paper introduces the features of the ft1780 audio processing chip, and describes its application examples on the mobile phone in detail.

Ft1780 chip internal structure and features

Figure 1 is an internal block diagram of the ft1780 chip. It can be seen that the ft1780 consists mainly of seven parts.

Figure 1: Internal block diagram of the ft1780 chip.

1. Host interface: connected to the Baseband, through which the Baseband sends commands and reads status to the ft1780.

2. Audio/System Engine: The core part of the chip, complete 64 chord MIDI synthesis, MP3 decoding, seven-band digital equalizer, file system management, system control and other functions;

3. SD/MMC card controller: complete the SD/MMC card interface function;

4. Input / output controller: complete I ² S interface, four LED control, motor and backlight control;

5. Power management system: It can turn off unused function modules and save system power consumption;

6. Stereo Headphone Amplifier: It can directly drive 16ohm headphones, and the output power can reach more than 20mW;

7. Speaker power amplifier: It can directly drive 8ohm speakers, and the output power can reach more than 500mW;

The ft1780 chip is available in a 6mm x 7mm 48Pin BGA package. Compared to other common MP3 decoder chips, it has the following main features:

1. The working current is small, and the power-saving design circuit is efficient. The modules in the chip can be individually controlled to open and close, which can meet different working mode requirements on the mobile phone;

2. Supports full range of sampling rate and encoding rate MP3 data, including MPEG Version1 Layer3, MPEG Version2 Layer3 and MPEG Version2.5 Layer3 standard, sampling rate range is 8~48kHz, encoding rate is 8~320kbps, decoding quality is high, sound Good sound quality;

3. Supports 64 chord ringtones, supports its own human sound format (FTF format), and supports natural and background sound playback;

4. The file management system program of the built-in SD/MMC card does not require the baseband of the mobile phone to parse the file system on the SD/MMC card. The baseband can control the playback function of the ft1780 by simply issuing a simple command. The data of the SD/MMC card can be Without the baseband, the ft1780 chip itself reads and plays, which can greatly reduce the burden of the baseband, and thus broaden the application of the ft1780.

5. Built-in high-quality stereo headphone power amplifier circuit, high output power, and headphone output circuit with no coupling capacitor design. Ordinary headphone output requires two large DC blocking capacitors. If the capacitor capacity is too small, the low frequency response will be poor and the sound will be distorted. The non-coupling capacitor design can save cost, save valuable space on the mobile phone circuit board, and increase the fidelity of the headphone output.

6. Built-in speaker power amplifier circuit, can output more than 500mW on 8ohm speakers.

Figure 2: Schematic diagram of a typical application.

Curved application of ft1780 chip

The application circuit of ft1780 is relatively simple, and there are few peripheral components required. Only a dozen resistors and capacitors are needed. Typical application lines are shown in 2. By adjusting the ratio of R1 and R3, the gain of the ft1780 internal output to the horn can be adjusted. By adjusting C1 and C3, the high frequency and low frequency characteristics of the horn output sound can be adjusted. For the parameters listed in the figure, R1=33k ohm, C1=330pF, R3=33k ohm, C3=0.1uF, increase Gain=R1/R3=1, high frequency cutoff frequency is F _H =1/(2*π*R1*C1)=14.6kHz, low frequency cutoff frequency is F _L =1 /(2*π*R3*C3)=48.2Hz. The audio signal coming in from Audio In can be controlled from the speaker or earphone, and its low frequency response curve can be adjusted via R2 and C2 as needed. In the figure, the output of the earphone has been designed with no coupling capacitor, so there is no output coupling capacitor on the picture, but it should be noted that the common end of the earphone is not the usual “ground”, and the virtual ground “HPR” on the chip is required. . In addition, the VDDA pin of the chip can be directly connected to the positive level of the battery. When the chip is not working, the software can be used to control the chip to enter the "Power Down" state, and the power consumption of the chip is only a few microamps.

Related software and playback process

The work of the ft1780 chip requires corresponding driver support. The driver adopts a modular structure, and each function has a corresponding program. In the Design In process, just modify the hardware-related address parameters, add the interrupt service program (you can also use the timer-related query mode), and then call the corresponding API. It works fine (sounds). Figure 3 is a schematic diagram of the software module, the following briefly introduces the functions of each module:

Figure 3: Schematic diagram of the software module.

1. Hardware platform related modules: It is necessary to modify the corresponding parameters according to the situation of the mobile phone platform, mainly including the operation address of the chip register, the frequency of the input clock, etc.

2. MIDI module: MIDI data parsing and processing, MIDI playback control and callback control;

3. ADPCM module: ADPCM data parsing and processing, ADPCM playback control and callback control;

4. FTF module: FTF data parsing and processing, FTF playback control and callback control;

5. SD/MMC module: SD/MMC command parsing and processing, SD/MMC playback control and callback control;

6. MP3 module: MP3 data parsing and processing, MP3 playback control and callback control;

7. Interrupt service module: corresponding processing of each interrupt event of the chip, mainly supplementing data, playing end control and error information processing;

8. Driver API module: Provides the call of the functions required by the user. The user does not have to care about the details of the specific underlying module, and only needs to deal with the upper API;

9. User Reference Module: An example of how to use the API to control playback. It can also be further packaged as an API for direct use by the user.

Below we introduce the use of ft1780 software.

The process of playing files on Baseband

Figure 4 is a flow chart for playing a file on a Baseband. When the user wants to play the audio data on the Baseband, firstly, the ft1780 chip is initialized, and then the data to be played is preprocessed. The driver analyzes the data format and automatically calls the underlying processing function according to the format. Then the next step is Start interrupt or timer, message and other mechanisms. The purpose of this step is to start the background processing task. When entering the playback state, the background task needs to complete the subsequent processing. Finally, the playback start command is issued, and the sound is played and the playback state is entered. .

Figure 4: Flowchart for playing a file on Baseband.

In the playback state, the ft1780 chip will issue an interrupt request according to the internal operation. The Baseband must process the corresponding event within a certain period of time, otherwise there will be sound pauses and discontinuities. Inside the ft1780 chip, there is a large FIFO (first in first out memory) to save the played data, which can adapt to the problem of low latency of the low-end Baseband interrupt response, ensuring smooth sound playback.

During playback, Baseband can call the corresponding API to stop the current playback, or read playback information, pause/resume, etc. at any time.

The process of playing files on SD/MMC card

Figure 5 is a flow chart for playing a file on an SD/MMC card. When the user wants to play the sound file on the SD/MMC card, firstly, the ft1780 chip is initialized, then the sound file on the card is read, the file to be played is selected, and the simple API play command is called to enter the playing state. The chip will automatically read the data on the card, play the sound, and then the next step is to start the interrupt or timer, message and other mechanisms. The purpose of this step is to start the background processing task and handle the interrupt transaction.

Figure 5: Flowchart for playing a file on an SD/MMC card.

Although it seems to be similar to the process of playing files on Baseband, there are mainly the following differences: When playing a file on Baseband, Baseband must continuously send data to the ft1780 chip, and the interruption will be more frequent (the code rate of the file being played back) Related), and when playing the file on the SD/MMC card, the ft1780 chip itself reads the required data from the SD/MMC card, does not require the intervention of the Baseband, basically does not interrupt the task during the playback, only at the end of the playback When the baseband is interrupted, Baseband is determined. Baseband decides the next work, such as repeating playback or playing the next file, so the requirements for Baseband are lower and the adaptability is wider.

During playback, Baseband calls the corresponding API function at any time to complete the function of stopping playback, suspending/restoring.