New voice compression codec AMBE2000

Abstract: AMBE2000 is a voice compression / decompression chip with patented technology launched by DVSI. The chip can be used for full-duplex compression and decompression, thereby providing high-quality voice quality with an extremely high compression rate. It introduces its main features, pin functions, control interface and application circuit.

1 Introduction

AMBE2000 is a high-performance, low-power single-chip real-time voice compression and decompression chip, the compression rate can be adjusted by software in the range of 2kbps ~ 9.6kbps, and has FEC (forward error correction), VAD (voice activation detection ) Function and DTMF signal detection function, so it can be widely used in satellite communications, digital mobile communications, confidential communications, voice mail, etc.

2 Pin description and characteristic parameters

The main characteristics and parameters of AMBE2000 are as follows:

● With high-quality voice quality;

● Compressed data rate can be adjusted by software in the range of 2kbps ~ 9.6kbps;

● The error correction rate ranges from 50bps to 7.2kbps;

● With VAD (Voice Activation Detection) / CNI (Insertion Comfort Noise) function;

● With DTMF signal detection and generation function;

● Power supply voltage: + 3.3V;

● Working temperature range: －40 ～ ＋ 100 ℃;

● Adopt 100 feet TQFP package.

Table 1 Host interface selection

Table 2 Voice data bit selection (unformatted)

The pin description of AMBE2000 is as follows:

CHANN_SEL0 ~ 1 (75, 77) feet: host interface type selection terminal? See Table 1 for specific operations;

BAUD_SEL0 ～ 1 (80 ～ 81) feet: unformatted voice data bit selection terminal? See Table 2 for specific operations?

RATE_SEL0 ~ 4 (70 ~ 74) feet: voice compression rate and forward error correction rate selection terminal? See Table 3 for specific operations;

CODEC_SEL0 ～ 1 (84 ～ 85) feet: A / D and D / A interface selection ports? See Table 4 for specific operations;

Table 3 AMBE2000 compressed data rate selection table

* Note: The compressed data rate can also be changed by the control word.

Table 4 A / DD / A hardware configuration

VAD_EN (86) foot: enable voice activation detection function terminal (active high level);

ECHOCAN_EN (78) foot: Enable the echo cancellation function terminal (active at high level);

SLEEP_EN (83) foot: Sleep mode control port (active high);

SLIP_EN (82) foot: Sliding mode control port (active high);

X2 / CLKIN (68) pin: 16.384MHz clock input pin;

X1 (67) feet: internal oscillator output;

RESET (69) pin: reset pin (active low);

EPR (20) foot: coding package ready flag;

SOFT_EN (79) foot: enable software error code judgment port (active high);

CHAN_RX_DATA (32) foot: used to receive host data to AMBE2000;

CHAN_TX_DATA (42) foot: used to send AMBE2000 data to the host;

CHAN_RX_LK (28) foot: the host receives the clock;

CHAN_TX_CLK (34) foot: the host sends the clock;

CHAN_TX_STRB (38) foot: the host sends / receives a frame synchronization pulse;

CHAN_RX_STRB (30) foot: the host receives the frame synchronization pulse port;

CODEC_RX_STRB (29) foot: A / D frame synchronization pulse receiving end;

CODEC_TX_STRB (37) foot: D / A frame synchronization pulse sending port;

CODEC_RX_DATA (31) foot: A / D sends PCM data to AMBE2000;

CODEC_TX_DATA (41) foot: AMBE2000 sends PCM data to D / A;

CODE_RX_CLK (27) feet: A / D clock;

CODEC_TX_CLK (33) foot: D / A clock;

CLOCK_MODE (51) pin: clock mode selection port, select crystal oscillation mode when this port is connected to high level; select external clock when connected to low level);

VDD (8, 11, 12, 23, 36, 39, 44, 45, 46, 47, 48, 49, 54, 57, 64, 76, 87, 90 feet): positive power supply;

GND (1, 9, 10, 25, 26, 35, 40, 50, 52, 53, 56, 63, 65, 88, 89 feet): ground terminal;

Other pins: N. C, don't use it in the air.

3. Host interface and data format

The interface data format between AMBE2000 and the host is divided into two types: one is formatted; the other is unformatted.

3.1 Formatted

In the case of a format, AMBE2000 generates a compressed data packet approximately every 20ms. This data packet is composed of 24 words; after the data packet is generated, its EPR pin will output a short negative pulse indication to determine the data Package handling. The specific composition of the data packet is as follows:

Format word 0: fixed to x13ECH, which is the header of the data packet;

Format word 1: The upper 8 bits are used for chip power control, 0x00 means normal working mode; 0x55 means low power consumption mode. The functions of the lower 8 bits (higher effective) are listed in Table 5;

Table 5 Format word 1 format

Table 6 Format words 2-6 format

Format words 2 to 6: used to specify and express the compressed data rate of the chip, as shown in Table 6;

Format word 7: This bit is not used in the input data packet, so it should be set to 0x0000 during design; and the bit error rate is indicated in the output data packet;

Format words 8 and 9: not used, usually set to 0x0000;

Format word 10: The upper 8 bits are used to control and indicate the amplitude of the DTMF signal, ranging from 3 to -60 dBM0 (for example: 0x03 = 3, 0x00 = 0, 0xC4 = -60); the lower 8 bits are used to control and detect the DTMF signal The signal sent and detected is a standard North American calling tone. The DTMF codes are listed in Table 7.

Table 7 DTMF codes

Table 8 Format word 11 format

Format word 11: The upper 8 bits are used for decoder volume control, where 0x80 represents the original volume, 0xFF is twice the original volume, and less than 0x80 is to reduce the volume; the functions of the lower 8 bits are listed in Table 8. The encoding / decoding options are as follows: 00 is encoding + decoding; 01 is encoding; 10 is decoding; 11 is not used;

Format words 12 ～ 23: compressed data information. The number of data bits varies according to the data rate. The relationship between the number of data bits and the compressed data rate is as follows:

Number of bits = compressed data rate (bps) / 50 (bps)

For example, at the lowest compression rate of 2kbps, the number of data bits is:

2000/50 = 40 digits.

3.2 Plain

In the case of no format, only the data bits need to be sent, but 50 bits of data per second will be reduced (compared to the formatted case), which will reduce the voice quality. See Table 2 for the number of data bits contained in each word. The relationship between the number of words per frame and the compressed data rate is as follows:

Number of words = [compressed data rate (bps) / 50 (bps)] / digits

In the formula, the selected number of digits must be divisible by the selected compressed data rate. The maximum clock rate of the AMBE2000 serial port is 2.048MHz.

Figure 1 Practical circuit for voice sampling, compression, and decompression composed of AMBE2000 and AD73311

4 Application circuit

Figure 1 shows a practical circuit for speech sampling, compression, and decompression formed by AMBE2000 and AD73311. Among them, AD73311 is a vocoder chip of A-DI. Its sampling rate can reach 32kHz, 16-bit sampling data, It has good sound quality, so it can be used with AMBE2000 and has achieved good results in practical applications. In the figure, the pin connection method selected by AMBE2000 defines the compression ratio as 2kbps? At the same time, the circuit is set in the external input clock mode, and the echo cancellation, voice activation, and slip compensation functions are effective. Its EPR pin is used to output the packet ready indicator signal. After the circuit is powered on and works normally, you can also reset the AMBE2000 through software. Therefore, the AMBE2000 voice compression codec is very flexible in application.

5 Conclusion

Voice communication occupies a very important position in digital communication. The data compression method composed of AMBE2000 and AD73311 introduced in this article can not only save storage resources, but also reduce the demand for communication bandwidth. Therefore, in some special application fields, AMBE2000 voice compression codec chip has very broad application prospects.

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