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SB3229 数据表(PDF) 8 Page - ON Semiconductor |
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SB3229 数据表(HTML) 8 Page - ON Semiconductor |
8 / 17 page RHYTHM SB3229 www.onsemi.com 8 Analog Inputs SB3229 provides for up to four analog inputs, Microphone 1 (MIC1), Microphone 2 (MIC2), Telecoil (TCOIL) and Direct Audio Input (DAI) with the following configurable front end modes: • MIC1 • MIC2 • DAI • TCOIL • MIC1 + TCOIL • MIC1 + DAI Attenuation can be applied to the MIC1 input when mixing with either TCOIL or DAI inputs. Analog input signals should be ground referenced to MGND. (Microphones, telecoils, DAI). MGND is internally connected to GND to minimize noise, and should not be connected to any external ground point. Channel Processing Figure 5 represents the I/O characteristic of independent AGC channel processing. The I/O curve can be divided into four main regions: • Low input level expansion (squelch) region • Low input level linear region • Compression region • High input level linear region (return to linear) Figure 5. Independent Channel I/O Curve Flexibility −100 −90 −80 −70 −60 −50 −40 −30 −20 −10 0 −120 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 INPUT LEVEL (dBV) Low Level Gain Compression Ratio High Level Gain Squelch Threshold Lower Threshold Upper Threshold Channel I/O processing is specified by the Squelch threshold (SQUELCHTH) and any four of the following five parameters (only four of the five properties are independent): • Low level gain (LLGAIN) • Lower threshold (LTH) • High level gain (HLGAIN) • Upper threshold (UTH) • Compression ratio (CR) During the Parameter Map creation, constraints are applied to the compression parameters to ensure that the I/O characteristics are continuous. Parameter adjustments support two popular styles of compression ratio adjustment: • The compression region of the I/O curve pivots about the upper threshold. As the compression ratio trimmer is adjusted, high−level gain remains constant while the low−level gain changes. • The compression region of the I/O curve pivots about the lower threshold. Low−level gain remains constant as the compression ratio trimmer is adjusted. The squelch region within each channel implements a low level noise reduction scheme (1:3 expansion) for listener comfort. This scheme operates in quiet listening environments (programmable threshold) to reduce the gain at very low levels. Automatic Telecoil The automatic telecoil feature in SB3229 is to be used with memory D programmed with the telecoil or MIC + TCOIL front end configuration. The feature enables the part to transition to memory D upon the closing of a switch connected to MS2. With the feature enabled and a reed switch connected to MS2, the static magnetic field of a telephone handset will close the switch whenever the handset is brought close to the device, causing the hybrid to change to memory D. The part will transition back to the initial memory once the switch is deemed opened after proper debouncing. A debounce algorithm with a programmable debounce period is used to prevent needless switching in and out of memory D due to physical switch bounces when MS2 is configured for automatic telecoil. Upon detecting a close to open switch transition, the debounce algorithm monitors the switch status. The debounce algorithm switches the device out of memory D only once the switch signal has been continuously sampled open over the specified debounce period. Adaptive Feedback Canceller The Adaptive Feedback Canceller (AFC) reduces acoustic feedback by forming an estimate of the hearing aid feedback signal and then subtracting this estimate from the hearing aid input. The forward path of the hearing aid is not affected. Unlike adaptive notch filter approaches, SM3229’s AFC does not reduce the hearing aid’s gain. The AFC is based on a time−domain model of the feedback path. The third−generation AFC (see Figure 6) allows for an increase in the stable gain1 of the hearing instrument while minimizing artefacts for music and tonal input signals. As with previous products, the feedback canceller provides completely automatic operation. 1. Added stable gain will vary based on hearing aid style and acoustic setup. Please refer to the Adaptive Feedback Cancellation Information note for more details |
类似零件编号 - SB3229 |
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类似说明 - SB3229 |
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