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Abstract: AMBE2000 is a patented voice compression/decompression chip introduced by DVSI. The chip is capable of full-duplex compression and decompression to provide high quality speech quality at very high compression rates. The main features, pin functions, control interfaces and application circuits are described in the paper.Keywords: speech compression; format word; FEC; VAD; AMBE2000
1 Introduction
AMBE2000 is a high-performance, low-power single-chip real-time voice compression decompression chip with a compression ratio ranging from 2kbps to 9.6kbps, with FEC (Forward Error Correction) and VAD (Voice Activation Detection). ) Function and DTMF signal detection function, so it can be widely used in satellite communication, digital mobile communication, secure communication, voice mail and so on.
2 pin description and characteristic parameters
The main features and parameters of AMBE2000 are as follows:
â— High quality voice quality;
â— The compressed data rate can be adjusted by software in the range of 2kbps to 9.6kbps;
â— The error correction rate ranges from 50bps to 7.2kbps;
â—With VAD (Voice Activation Detection) / CNI (Insert Comfort Noise) function;
â— With DTMF signal detection and generation function;
â—Power supply voltage: +3.3V;
◠Operating temperature range: -40 ~ +100 ° C;
â— It is packaged in a 100-pin TQFP.
Table 1 Host Interface Selection
| Port type | Select foot | |
| CH_SEL1 | CH_SEL0 | |
| Active format | 0 | 0 |
| Active unformatted | 0 | 1 |
| Passive format | 1 | 0 |
| Passive plain | 1 | 1 |
Table 2 Voice data bit selection (no format)
| Number of voice data bits in the word | Select foot | |
| BA_SEL1 | BA_SEL0 | |
| 1 | 0 | 0 |
| 2 | 0 | 1 |
| 3 | 1 | 0 |
| 4 | 1 | 1 |
The pin descriptions for the AMBE2000 are as follows:
CHANN_SEL0~1 (75,77) feet: host interface type selection terminal? The specific operation is listed in Table 1;
BAUD_SEL0~1 (80~81) feet: Unformatted voice data bit selection terminal? See Table 2 for details.
RATE_SEL0~4 (70~74) feet: speech compression rate and forward error correction rate selection end? The specific operations are listed in Table 3;
CODEC_SEL0~1 (84~85) feet: A/D and D/A interface select ports? The specific operations are listed in Table 4;
Table 3 AMBE2000 compressed data rate selection table
| Pin 74 | Pin 73 | Pin 72 | Pin 71 | Pin 70 | Speech rate (bps) | FEC rate (bps) | Total data rate (bps) |
| 1 | 1 | 1 | 1 | 1 | 2000 | 0 | 2000 |
| 1 | 0 | 0 | 0 | 0 | 3600 | 0 | 3600 |
| 1 | 0 | 0 | 0 | 1 | 4000 | 0 | 4000 |
| 1 | 0 | 1 | 1 | 0 | 2400 | 1600 | |
| 1 | 0 | 0 | 1 | 0 | 4800 | 0 | 4800 |
| 1 | 1 | 0 | 0 | 0 | 4000 | 800 | |
| 1 | 0 | 1 | 1 | 1 | 3600 | 1200 | |
| 1 | 1 | 0 | 0 | 1 | 2400 | 2400 | |
| 1 | 0 | 0 | 1 | 1 | 6400 | 0 | 6400 |
| 1 | 1 | 0 | 1 | 0 | 4000 | 2400 | |
| 1 | 1 | 0 | 1 | 1 | 4400 | 2800 | 7200 |
| 1 | 0 | 1 | 0 | 0 | 8000 | 0 | 8000 |
| 1 | 1 | 1 | 0 | 0 | 4000 | 4000 | |
| 1 | 0 | 1 | 0 | 1 | 9600 | 0 | 9600 |
| 1 | 1 | 1 | 0 | 1 | 3600 | 6000 | |
| 1 | 1 | 1 | 1 | 0 | 2400 | 7200 |
*Note: The compressed data rate can also be changed by the control word.
Table 4 A/DD/A hardware configuration
| A/DD/A type | CODEC_SEL1 | CODEC_SEL0 |
| Normal 16-bit linear (sampling rate 8 kHz) | 0 | 0 |
| AD company AD73311 (sampling rate 32kHz) | 0 | 1 |
| Ordinary μ law (sampling rate 8 kHz) | 1 | 0 |
| Normal A law (sampling rate 8 kHz) | 1 | 1 |
VAD_EN (86) pin: Enable voice activation detection function (active high);
ECHOCAN_EN (78) pin: Enable echo cancellation function (active high);
SLEEP_EN (83) pin: Sleep mode control port (active high);
SLIP_EN (82) pin: Sliding mode control port (active high);
X2/CLKIN (68) pin: 16.384MHz clock input pin;
X1 (67) pin: internal oscillator output;
RESETN (69) pin: reset pin (low active);
EPR (20) foot: coding package ready flag;
SOFT_EN (79) pin: Enable software error judgment port (active high);
CHAN_RX_DATA (32) pin: used to receive host data to AMBE2000;
CHAN_TX_DATA (42) pin: used to send AMBE2000 data to the host;
CHAN_RX_LK (28) pin: The host receives the clock;
CHAN_TX_CLK (34) pin: The host sends a clock;
CHAN_TX_STRB (38): The host sends/receives a frame sync pulse;
CHAN_RX_STRB (30) pin: The host receives the frame sync pulse port;
CODEC_RX_STRB (29) pin: A/D frame sync pulse receiving end;
CODEC_TX_STRB (37) pin: D/A frame sync pulse transmission port;
CODEC_RX_DATA (31): A/D sends PCM data to AMBE2000;
CODEC_TX_DATA (41) pin: AMBE2000 sends PCM data to D/A;
CODEC_RX_CLK (27) pin: A/D clock;
CODEC_TX_CLK (33) pin: D/A clock;
CLOCK_MODE (51) pin: Clock mode select port, select the crystal oscillation mode when the port is connected to the high level; select the external clock when connected to the 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;
The remaining pins: N. C, no need to hang.
3 host interface and data format
There are two types of interface data formats between AMBE2000 and the host: one is formatted; the other is unformatted.
3.1 formatted
In the case of format, AMBE2000 generates a compressed data packet every 20ms. This data packet consists of 24 words. After the data packet is generated, its EPR pin will output a short negative pulse indication, which will determine the data. The processing of the package. The specific composition of the data packet is as follows:
Format word 0: fixed to x13ECH, which is the header of the packet;
Format Word 1: High 8 bits for chip power control, 0x00 for normal operation mode, and 0x55 for low power mode. The lower 8 bits function (high effective) is listed in Table 5;
Table 5 format word 1 format
| Types of | 7: MSB | 6 | 5 | 4 | 3 | 2 | 1 | 0: LSB |
| enter | Make up lost frames | NC | NC | NC | NC | NC | Insert comfort noise | NC |
| Output | NC | NC | Decoding frame repetition | Decoding silence indication | NC | NC | Coded silence detection | Coded DTMF detection |
Table 6 format word 2-6 format
| Word 2 | Word 3 | Word 4 | Word 5 | Word 6 | Speech rate (bps) | FEC rate (bps) | Total data rate (bps) |
| 0x0028 | 0x0000 | 0x0000 | 0x0000 | 0x6428 | 2000 | 0 | 2000 |
| 0x5048 | 0x0000 | 0x0000 | 0x0000 | 0x3948 | 3600 | 0 | 3600 |
| 0x5250 | 0x0000 | 0x0000 | 0x0000 | 0x4150 | 4000 | 0 | 4000 |
| 0x1030 | 0x0001 | 0x0000 | 0x34la | 0x6750 | 2400 | 1600 | |
| 0x5360 | 0x0000 | 0x0000 | 0x0000 | 0x6c60 | 4800 | 0 | 4800 |
| 0x5250 | 0x2010 | 0x0000 | 0x0000 | 0x7460 | 4000 | 800 | |
| 0x5048 | 0x0001 | 0x0000 | 0x2412 | 0x6860 | 3600 | 1200 | |
| 0x1030 | 0x0005 | 0x180c | 0x3018 | 0x7360 | 2400 | 2400 | |
| 0x6b80 | 0x0000 | 0x0000 | 0x0000 | 0x6c80 | 6400 | 0 | 6400 |
| 0x5250 | 0x0001 | 0x0000 | 0x542a | 0x5280 | 4000 | 2400 | |
| 0x5258 | 0x0009 | 0xle0c | 0x4127 | 0x7390 | 4400 | 2800 | 7200 |
| 0x7fa0 | 0x0000 | 0x0000 | 0x0000 | 0x52a0 | 8000 | 0 | 8000 |
| 0x5250 | 0x0005 | 0x2010 | 0x6834 | 0x72a0 | 40000 | 4000 | |
| 0x7fc0 | 0x0000 | 0x0000 | 0x0000 | 0x69c0 | 9600 | 0 | 9600 |
| 0x5048 | 0x000e | 0x4010 | 0x6a2e | 0x65c0 | 3600 | 6000 | |
| 0x1030 | 0x000e | 0x68la | 0x511b | 0x76c0 | 2400 | 7200 |
Format words 2 to 6: used to specify and represent the compressed data rate of the chip, as listed in Table 6;
Format word 7: This bit is not used in the input packet, so it should be set to 0x0000 at design time and the bit error rate in the output packet;
Format words 8, 9: not used, usually set to 0x0000;
Format Word 10: The upper 8 bits are used to control and represent the amplitude of the DTMF signal, ranging from 3 to -60 dBm0 (eg: 0x03=3, 0x00=0, 0xC4=-60); the lower 8 bits are used to control and detect the DTMF signal. The signals emitted and detected are standard North American calling tones. The DTMF codes are listed in Table 7.
Table 7 DTMF code
| DTMF code | DTMF number | DTMF code | DTMF number |
| 0x80 | 1 | 0x84 | 2 |
| 0x88 | 3 | 0x81 | 4 |
| 0x85 | 5 | 0x89 | 6 |
| 0x82 | 7 | 0x86 | 8 |
| 0x8A | 9 | 0x87 | 0 |
| 0x83 | * | 0x8B | # |
| 0x8C | A | 0x8D | B |
| 0x8E | C | 0x8F | D |
| 0xFF | DTMF is invalid |
Table 8 Format Word 11 Format
| Types of | 7: MSB | 6 | 5 | 4 | 3 | 2 | 1 | 0: LSB |
| enter | NC | NC | Voice activation (1) | NC | Sleep (1) | Echo cancellation (1) | Encoding/decoding selection | |
| Output | NC | NC | NC | NC | Sleep (1) | Echo cancellation (1) | Encoding/decoding selection | |
Format Word 11: The upper 8 bits are used for the decoder volume control, where 0x80 represents the original volume, 0xFF is twice the original volume, and less than 0x80 is the volume reduction; the lower 8 bits are listed in Table 8. The encoding/decoding is selected as follows: 00 is encoding + decoding; 01 is encoding; 10 is decoding; 11 is not used;
Format words 12 to 23: Compress data information. The number of data bits varies depending on 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 a minimum compression ratio of 2 kbps, the number of data bits is:
2000/50=40.
3.2 Unformatted
In the case of no format, only the data bits need to be transmitted, but the data is reduced by 50 bits per second (compared to the formatted case), thus degrading the voice quality. See Table 2 for the number of bits of data contained in each word. The relationship between the number of words per frame and the compressed data rate is as follows:
Word count = [compressed data rate (bps) / 50 (bps)] / number of digits
In the formula, the selected number of bits must be divisible by the selected compressed data rate. The AMBE2000 serial clock rate is up to 2.048MHz.
Figure 1 Practical circuit for speech sampling, compression and decompression composed of AMBE2000 and AD73311
4 application circuit
Figure 1 shows a practical sampling circuit for compressing, compressing and decompressing the AMBE2000 and AD73311. The AD73311 is a vocoder chip of A-DI, which can sample data at 32 kHz and 16 bits. It has good sound quality and can be used with AMBE2000. It has achieved good results in practical applications. In the figure, the pin connection 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 sliding compensation functions are valid, and the EPR pin is used to output the packet ready indication signal. After the circuit is powered up, the AMBE2000 can also be reset by software. Therefore, the AMBE2000 voice compression codec is very flexible to apply.
5 Conclusion
Voice communication plays an important role in digital communication. The data compression method formed by AMBE2000 and AD73311 described in this paper can not only save storage resources, but also reduce the need for communication bandwidth. Therefore, in some special application fields, AMBE2000 voice compression codec chip has a very broad application prospect.
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