This article refers to the address: http:// The space constraints of the handheld product structure are increasing, the speakers are getting smaller and smaller, the required sound is getting louder and louder, and various noises and echoes are suppressed (linear, nonlinear echoes during video hands-free calling), in noise Achieving clear voice communication in the environment is a problem that is facing problems. Figure 1 Anti-noise diagram of SAM handheld mode Figure 2 Anti-noise diagram of SAM hands-free mode Mini Array Microphone Technology Design Essentials Figure 3 Microphone placement Figure 4 SAM's cone-shaped pickup beam suppresses noise effect Figure 5 SAM cone-shaped pickup beam pattern sound effect Figure 6 Application diagram of FM2010 in TI mobile phone platform Figure 7 Typical application schematic of FM2010 Figure 8 call mode control process Figure 9 Test mode control flow Neodymium Magnetic Bar,Neodymium Magnets,Permanent Magnet Bar Ningbo Wewinmagnet Co.,Ltd , http://www.wewinmagnet.com
The FM2010 chip from ForteMedia is based on the patented Mini Array Microphone (SAM) technology, which uses spatial filtering technology to pick up sound signals in far/close range, suppress acoustic noise, and eliminate low acoustics. The cost of a single chip. This article will introduce the design points of mini-array microphone technology in handheld communication products, the main functions of FM2010 chip, and its typical application in GSM mobile phones. FIG. 1 is a schematic diagram of anti-noise of the handheld mode; FIG. 2 is a schematic diagram of anti-noise of the hands-free mode.
The SAM technology can use a Uni-MIC (primary microphone) and an Omni-MIC (reference microphone) to form a mini-array microphone, placed back-to-back or side-to-side, as shown in Figure 3. Using the difference in physical characteristics of the two microphones, after processing by the FM2010 chip, a cone-shaped pickup beam is formed to form a spatial filter for suppressing unsteady noise. The characteristics of the microphone, the structural design and the parameter adjustment of the FM2010 determine the direction, angle and effect of suppressing the unsteady noise of the cone pickup beam.
1 microphone selection
A 4mm Uni, Omni microphone is recommended. Uni-MIC sensitivity is -40dB ±3dB; spectrum is less than 8.5dB at 300Hz, 3.4kHz is less than 3.5dB; directivity is heart-shaped, directional 0° and 90° sensitivity difference is greater than 4dB, 0° and 180° sensitivity The difference is greater than 10dB. The Omni-MIC has a sensitivity of -40dB ± 1.5dB; the spectrum is flat from 300Hz to 3.4kHz. It is recommended to use the Uni microphone B4015UL403 and Omni microphone B4015AL-398 from Shandong Weifang Yilida (IEA).
2 structural design
The key issue in structural design is the maintenance of the characteristics of the Uni microphone and the direction of the cone-shaped pickup beam. If there is a hands-free calling function, more consideration should be given to the speaker, microphone damping and microphone airtightness. The direction of the cone-shaped pickup beam determines the direction in which the unsteady noise is suppressed, so it should be ensured that the useful signal is within the pickup beam, otherwise it will be suppressed as noise. Therefore, in the design of the product shape, the direction of the Uni microphone should be fully considered. The structural design should ensure that the sensitivity difference between 0° and 180° is greater than 6dB after the Uni microphone is loaded into the microphone sleeve and the entire casing, and the sensitivity and frequency characteristics are basically unchanged. Microphone damping can reduce nonlinear echo, which can reduce linear echo and improve the signal echo ratio of the system.
3 Signals processed by FM2010
The signal picked up by the mini array microphone and the signal output after FM2010 processing are compared as shown in Fig. 4. The sound source is 0.3m from the mini-array microphone and has a sound intensity of 83dB (SPL). The test signals are the signals output by the FM microphones of the Uni microphones 0° and 180°, the Omni microphones 0° and 180°, and the line output (Lout) mini-array microphones 0° and 180°. As can be seen from Fig. 4, the signals of the same size, the signals finally output in the pickup beam (0°) and the outside of the pickup beam (180°) can be different by 20 dB. That is to say, as long as the unsteady noise is outside the pickup beam, it will be suppressed by 20 dB with respect to the useful signal. The cone-shaped pickup beam has an effective range of 2 m. The angle of the SAM cone-shaped pickup beam depends on the pointing characteristics of the Uni microphone and the parameter adjustment of the FM2010. FIG. 5 is a cone-shaped pickup beam pattern of the actual test SAM.
Application of FM2010 in GSM mobile phone
FM2010 uses low power consumption and small size design, power consumption is less than 25mW, integrated DSP, CODEC, ROM and RAM on-chip, suitable for mobile handheld applications.
Take TI's mobile phone platform as an example. As shown in Figure 6, the FM2010 and analog baseband processor have four main interfaces: RECEIVER echo cancellation reference signal (HS REF), hands-free speaker echo cancellation reference signal (HF REF), Array microphone power and control (MIC PWR), array microphone signal output signal (LOUT) processed by FM2010. There are six main interfaces of FM2010 and digital baseband processor: clock signal (13MHz), SHI interface selection control (SHI_S), SHI interface (SHI), pass mode selection control (IRQ_ANA), reset control (RESET) and power saving control ( PWD).
The signals picked up by the Uni microphone and the Omni microphone are amplified by the programmable gain amplifier, analog-to-digital converted, and high-pass filtered, and sent to the speech processor for processing (linear echo cancellation, nonlinear echo cancellation, VAD detection, noise suppression processing, microphone volume setting), output. After the digital data conversion, the microphone signal is sent from the line output single-ended output to the TWL3014/16 analog baseband processor microphone input (MICIP/MIC1N), and processed by the uplink processing to the digital baseband processor OMAP733/750. . After receiving the signal, the GSM mobile phone is demodulated and decoded by the signal digital baseband processor OMAP733/750. After the confidential processing, the digital audio signal is sent to the TWL3014/16 analog baseband processor, and the downlink processing is performed from the receiver (HSO) and the earphone. (EARP/EARN) output, send the receiver all the way, send the external power amplifier to amplify, drive the hands-free speaker, and send the two signals to the line input of FM2010 respectively, convert the analog-to-digital conversion and high-pass filter into voice data, and send the voice processor. Processed as an echo reference signal. A typical application is shown in Figure 7.
FM2010's working mode in GSM mobile phone can be set according to needs, mainly including test mode, handheld noise canceling mode, hands-free conference mode, hands-free personal-only mode. The test mode is mainly used for mobile audio test (Acoustics). At this time, FM2010 is set to enter the pass-through mode (IRQ_ANA). FM2010 only amplifies the Uni microphone signal, and does not do any other processing, output from the line output pin; handheld noise canceling mode FM2010 Two microphone SAM modes working in Uni and Omni microphones are used to eliminate steady-state and unsteady noise in the call environment; hands-free conference mode is used in small multi-person conference mode, at this time FM2010 works in microphone inversion mode, FM2010 Amplify the signal of the Omni microphone to eliminate the steady-state echo in the call environment, output from the line output pin, the microphone can pick up the omnidirectional signal; the hands-free personal mode can be used for a conference occasion or video call used by one person.
OMAP733/750 control flow of FM2010: The operation of FM2010 is realized by SHI interface, PWD, RESET, ANA_IRQ control pin. After the whole machine is powered on, first set PWD high, ANA_IRQ is set low, after reset, send parameters to FM2010, mainly clock source, clock frequency, DSP working speed, and then put the chip into power saving mode. As shown in Figure 8, the call mode is based on whether there is a phone call in, out or recording operation, wake up FM2010, and after reset, send FM2010 corresponding mode parameters according to the handheld/hands-free mode. For handheld noise cancellation mode, the number of microphones, microphone gain, microphone volume, cancellation parameters, and VAD parameters are required. For the hands-free conference mode, the number of microphones to be sent, the microphone gain, the microphone volume, the microphone inversion, and the cancellation parameters (mainly including the other party's small voice, normal speech, loud speech). The hands-free personal-only mode debugging method is basically the same as the handheld noise-cancelling mode, and the echo cancellation parameters require more adjustments. After the call ends, turn off the FM2010's CODEC and set FM2010 to the power saving mode. As shown in Figure 9, the GSM mobile phone audio test mode is mainly used for mobile phone testing purposes. After entering the test mode, the FM2010 works in the pass-through mode. At this time, the internal DSP does not perform any processing on the microphone input signal. The Uni microphone input signal is amplified by the programmable gain amplifier and directly output from the LOUT amplifier, and can be connected to the microphone amplifier through the SHI interface. LOUT amplifier gain parameter.
FM2010 SHI interface control timing: SHI interface works in slave mode, externally provides clock signal, maximum clock frequency is 400kHz. When mode and parameter setting for FM2010, first send a transmission start state, then send 1 byte SHI device address C0, 2-byte sync word FCF3, then control command word 3B, 2-byte parameter address, 2-byte parameter data, repeat and then control command word 3B, 2-byte parameter address, 2-byte parameter data, and finally start The command control command word 3B, 2 bytes parameter address 1E 3A, 2 bytes parameter data 00 00 ends, let FM2010 run normally.