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ADMP441, SSM2529 Speech transmission



		

			

									
					    Eystein
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Feb 19, 2013 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I am constructing a hearing aid for my bachelor degree project. This hearing aid will consist of a microphone with a Nordic Semiconductor nRF2460 2.4 GHz transmitter, and a receiver of samë model with a speaker. This device should filter out any unwanted frequencies outside of speech, that is anything outside of 1-5 kHz. We want to sample at 12 kHz. I and my group are designing the PCB's and power supply ourselves. For simplicity we want mostly digital signals on our PCB's. Therefore we want to use the ADMP441 which has an ADC included with an I2S interface. Our transmitter and receiver (which are the same IC), support 16 bit I2S. The SSM2529 will be our DAC and amplifier stage, and also the filter stage.
    
 
    The question is, can I use the ADMP441, which supports 24 bit, to send a 16 bit signal to my 16 bit compatible transmitter?
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



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                on Mar 13, 2013 3:28 AM
            
            
					
        
	
        

		
		
        
					
        Okay, I ordered 2 of the AD1938. I'm thinking of using a TDA2822M as a power amp for my 4 ohm speaker. I figured since the AD1938 requires filtering before audio output, I would filter out anything outside of speech frequencies after the DAC stage. At page 30 in the AD1938 datasheet you recommend what appears to be a Sallen-Key lowpass filter. I am however unsure of what the components to the right of node 1, at the output of the opamp, are for. Could you explain this? 
        
 
        Also, is it necessary to use an active filter (maybe it helps to reduce noise, create buffer for impedances)?
        
 
        Thanks!
        
 
        - Eystein
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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													0
							
			
				
									
							        
			
			
			
          
            
			                            
                        
                on Mar 13, 2013 3:28 AM
            
            
					
          
	
          

		
		
          
					
          Okay, I ordered 2 of the AD1938. I'm thinking of using a TDA2822M as a power amp for my 4 ohm speaker. I figured since the AD1938 requires filtering before audio output, I would filter out anything outside of speech frequencies after the DAC stage. At page 30 in the AD1938 datasheet you recommend what appears to be a Sallen-Key lowpass filter. I am however unsure of what the components to the right of node 1, at the output of the opamp, are for. Could you explain this? 
          
 
          Also, is it necessary to use an active filter (maybe it helps to reduce noise, create buffer for impedances)?
          
 
          Thanks!
          
 
          - Eystein
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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