Abstract : AMBE-1000 is a good quality voice compression multi-rate speech coding / decoding chip . TLC32044 is dynamically adjustable high-precision 14-bit programmable A / DD / A chip . This article describes the AMBE-1000, TLC32044 performance features , working principle and interface circuits , and gives voice compression system application examples. Key words : AMBE-1000 vocoder TLC32044 voice compression 1 Overview Constitute the basis of the analysis of voice , emerged a variety of audio signal compression algorithms such as CELP, RELP, VSELP, MP-MLQ, LPC-10MBE so , they adopted a different algorithm to achieve the compression of audio signals . The compression algorithm of the compression ratio , voice quality of their own strengths, including the United States DVSI (Digital Voice System. Inc) companies advanced multi-band excitation AMBE (Advanced Multi-Band Excitation) coding algorithm is one of the outstanding representatives . AMBE is based on the MBE technique at low bit rate , high-quality voice compression algorithm, and the code has a good voice quality and low baud rate , and planted DVSI ‘s AMBE-1000 voice compression chip . The chip is a high performance multi-rate speech coding / decoding chip , the speech coding / decoding speed can be 2400 ~ 9600b / s , with a 50b interval changes . In a separate chip voice encoding and decoding channel , which can complete the task of speech coding and decoding ; and all the encoding and decoding operations are completed in the chip without external expanded memory . AMBE-1000 , these features make it very suitable for digital voice communications , encrypted voice communications and other needs of the digital voice processing occasions. 2 AMBE-1000 works , and hardware interface 2.1 Basic Workflow Simply put , AMBE-1000 ‘s working process shown in Figure 1 . AMBE-1000 can be viewed as two separate encoder and decoder. 8kHz voice encoder receives the data sample stream (such as 16-bit linear, 8-bit or 8-bit A law U Law ) and the output of a desired channel baud rate data stream . Instead, the channel decoder receives a data stream and synthesized a voice data stream . AMBE-1000 encoder and decoder interface timing is completely asynchronous. 2.2 -channel interfaces Channel Interface is used to describe the output from the encoder and the input compressed bit stream to the decoder, the compressed bit stream . The interface can also output status information , for example, can detect whether there is dual tone multi -frequency (DTMF) voice signal input . In addition , the interface of the encoder / decoder to perform more complex control operations (usually at initialization time ) . The control functions include error correction code rate of voice and choice , A / DD / A chip device. In most of the voice transmission system , the actual encoded bit stream to a certain format, extract out from the channel and system information , and together constitute the system to transmit data streams sent through the transmission channel ; at the receiving end is extracted out through the decoder Constitute the AMBE-1000 data stream format required . AMBE-1000 has a variety of operating modes: parallel and serial , with frame and without frame format , active and passive . Among them, the parallel passive frame mode is the most flexible and practical working pattern . Through the pull-up resistor and the allocation of position switch and the corresponding interface selection pin connected , you can select the appropriate mode . By using the above method , you can select the switch through the 2400 ~ 9600b / s and 50 ~ 4750b / s voice rate between free choice and error correction code rate . Active mode in the serial , AMBE-1000 the work of the clock as 27MHz, CHS_O_CLK clock to 4.5MHz (27MHz / 6), that domestic demand in 0.22µs read a data . Even if the work in the 24MHz MCU , the can not read the data , it shall be in passive mode , so you can set your clock CHS_O_CLK may also need to meet the clock can be read within 20ms 34 bytes of data (that is, a Data) ; also take up more parallel port interface resources , so it frames the serial passive mode , the hardware connection shown in Figure 2 . 2.3 Data Format AMBE-1000 data in a frame format , each frame composed of 17 characters . Encoder output of 17 words per 20ms , while the decoder will have to receiving 17 words . Each frame of the first 5 characters from the frame mark (Header), identification mark (ID), state ( output) or control (input ) information component , the remaining 12 characters to form encode / decode the data . The 12 words of 192 AMBE-1000 to 9600b / s maximum data rate mode of work (192b / frame × 50?/ s = 9600b / s). When the encoding / decoding data rate of less than 9600b / s , the shortage of spaces fill 0 . Note that , no matter what AMBE-1000 work rate, all 272 (17 word × 16b = 272b) of the frame data (including any unused at the end of zero ) must be output or input from the encoder decoder . No frame format used in serial mode only . Click to enlarge 2.4 AMBE-1000 and the interface circuit TLC32044 AMBE-1000 required A / D, D / A ‘s voice data and the way the serial input and output . The circuit is the key voice and data frame synchronization , the hardware interface circuit shown in Figure 3 . Work as TLC32044 which 5.184MHz clock , but also as a D flip-flop of the trigger pulse . Shift generated by the TLC32044 pulse (SHIFT CLK), used to implement bit synchronization transmission . By setting C_SEL0-2 for the 010 , to select TLC32044 chip . 2.5 Clock and reset AMBE-1000 the work of the clock for the 26 ~ 30MHz. It has three kinds of input : TTL clock source directly , CMOS clock source or oscillator directly , using a crystal oscillator input . In this system, the clock uses a crystal oscillator input . Reset signal is low , and have continued for more than six clock cycles . 3 peripheral interface circuits 3.1 TLC32044 works Digital speech signal processing and ultimately voice signal A / D and D / A converter . In this design, the use of a U.S. company TI Dynamic adjustable high-precision 14-bit programmable A / D, D / A ‘s TLC32044 chip . Shown in Figure 4 , TLC32044 by the anti- aliasing input filter , A / D, D / A, output reconstruction filters and other components. Analog and digital ground , analog and digital power of the separation can reduce the noise and ensure a wide dynamic range. Analog part of the differential circuit in order to minimize noise . TLC32044 also has a programmable sampling frequency , the sampling frequency is 7.2kHz ~ 19.2kHz in the range of software control , it can work in synchronization word , the word byte transmission and asynchronous , byte transmission working condition 4 , respectively 16bit 8bit byte word or serial communication , the highest conversion precision with 14bit , just outside a 5.184MHz clock will work . The chip can be programmed to accommodate two analog inputs . System power (or reset ) after the work is its default mode , namely by 16bit or 8bit byte word serial communication , the highest conversion precision with 14bit , just outside a 5.184MHz clock will work . The chip is programmed to accommodate two simultaneous analog inputs . System power (or reset ) after the work is its default mode , namely synchronous serial communication according to 16bit words , the sampling frequency of 8kHz. To change TLC32044 work status , can be programmed and the control word sent by the DX pin TLC32044. Figure 6 4 System Analysis Voice compression system block diagram shown in Figure 6 . The system will be free to choose their work rate . Active with the frame in the serial mode . AMBE-1000 can be a serial input and output pin shorted with each other , for system self-test to confirm the system is working. In system design , analog to note the distinction between ground and digital ground to avoid the introduction of background noise . The circuit design has been used in intelligent communication terminal end of speech compression can reduce the amount of voice data , while increasing the voice of confidentiality. The circuit can also be used when the solid cover machine , only the Flash chips with rewritable and control button.