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CS6422-IS 数据表(PDF) 10 Page - Cirrus Logic |
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CS6422-IS 数据表(HTML) 10 Page - Cirrus Logic |
10 / 48 page CS6422 10 2. OVERVIEW The CS6422 is a full-duplex speakerphone chip for use in hands-free communications with telephony quality audio. Common applications include speakerphones, inexpensive video-conferencing, and hands-free cellular phone car kits. The CS6422 requires very few external components and allows system control through a microcontroller interface. Hands-free communication through a microphone and speaker typically results in acoustic feedback or howling because the loop gain of the system ex- ceeds unity by the time audio amplitudes are ad- justed to a reasonable level. The solution to the howling problem has typically been half-duplex, where either the transmit or the receive channel is active, never both at the same time. This prevents instability, but diminishes the overall communica- tion quality by clipping words and forcing each talker to speak in turn. Full-duplex conversation, where both transmit and receive channels are active simultaneously, is the conversation quality we enjoy when using hand- sets. Full-duplex for hands-free communications is achieved in the CS6422 using a digital signal pro- cessing technique called “Echo Cancellation.” The end result is a more natural conversation than half- duplex, with no awkward breaks and pauses, allow- ing both parties to speak simultaneously. Echo Cancellation reduces overall loop gain and the acoustic coupling between speaker and micro- phone. This coupling reduction prevents the annoy- ing effect of hearing one’s own delayed speech, which is worsened when there is delay in the sys- tem, such as vocoder delay in digital cellular phones. The CS6422 is a complete system implementation of a Digital Signal Processor with RAM and pro- gram ROM, running Echo Cancellation algorithms developed at Crystal Semiconductor using custom- er input, integrated with two delta-sigma codecs. The CS6422 is intended to provide a full-duplex speakerphone solution with a minimum of design effort while displacing existing half-duplex speak- erphone chips. 3. FUNCTIONAL DESCRIPTION The CS6422 is divided into four external interface blocks. The analog interfaces connect the device to the transmit and receive paths. Control functions are accessible through the microcontroller inter- face. Two pins accommodate either a crystal or an externally applied digital clock signal. Analog and digital power and ground are provided through four pins. 3.1 Analog Interface In a speakerphone application, one input of the CS6422 connects to the signal from the micro- phone, called the near-end or transmit input, and one output connects to the speaker. The output that leads to the speaker is called the near-end or re- ceive output. Together, the input and output that connect to the microphone and speaker form the Acoustic Interface. The signal received at the near-end input is passed to the far-end or transmit output after acoustic echo cancellation. This signal is sent to the telephone line. The signal from the telephone line is received at the far-end input, also called the receive input, and this signal is passed to the receive output after network echo cancellation. The far-end input and output form the Network Interface. The analog interfaces are physically implemented using delta sigma converters running at an output word rate of 8 kHz, resulting in a passband from DC to 4 kHz. Because the inputs are analog to dig- ital converters (ADCs), anti-aliasing and full-scale input voltage must be kept in mind. The ADCs ex- pect a single-pole RC filter with a corner at 8 kHz, and they are post-compensated internally to pre- vent any resulting passband droop. The ADCs also expect a maximum of 0.9 Vrms (2.5 Vpp) at their in- puts (which are biased around 2.12 VDC). A signal CS6422 10 DS295F1 |
类似零件编号 - CS6422-IS |
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类似说明 - CS6422-IS |
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