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Choosing an amplifier for 0,1MHz to 10MHz +-3,6V signal generator



		

			

									
					    ElectronHunter
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 15, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi,
    

    I need to generate a signal that ranges from +-0,2v to +-3,6Vpp (symetrical to 0V) and has a frequency adjustable from 0,1MHz to 10MHz.
    

    Waveform shall be a nice square with fast rise and fall time.
    

    Frequency can be generated by LTC1799, but if there are better suited parts (faster rise and fall), I'd be very happy to know about it.
    

    What I don't know how to achieve is the Vpp adjusting part. All amplifiers I found having big enough slew rates are current feedback amplifiers and I once tried taming one and failed.
    

    

    I would also be happy with a completely different approach, like switching polarity off an adjustable voltage source via fast FETs
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
			                            
                        
                on Mar 16, 2022 3:13 AM
            
            
					
      
	
      

		
		
      
					
      Hi ElectronHunter,
      

      You may want to check High-Speed Op Amps Parametric Table: www.analog.com/.../11087 . This table contains SR specification for your requirement. Selecting a SR with more than 230V/uS would be good for your design. I used the formula SR = 2pi(BW)(Vpk) to get the minimum SR for your design. You may want to check this part - AD829: https://www.analog.com/en/products/ad829.html . Let me know if you have other questions.
      

      Hope this helps!
      

      Thanks,
      

      Kristine
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Mar 16, 2022 7:15 AM
            
            
												
						in reply to kristinehoffman
					
									
        
	
        

		
		
        
					
        Hi Kristine,
        

        Thank you for our answer.
        


        I have no idea who invented that formula, but 0,2V/ns is way too slow to get a proper 10MHz 5Vpp square signal.
        Simulation with LTSpice showed that at least a few kV/µs are needed do get adequate waveforms
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        
            
			                            
                        
                on Mar 16, 2022 8:32 AM
            
            
												
						in reply to ElectronHunter
					
									
        
	
        

		
		
        
					
        Hi Electronhunter,
        

        I see. Apologies for I assumed that your signal is sinusoidal where the formula I mentioned is applicable. Correct me if I'm wrong on my understanding with your requirements. With 10MHz duty cycle and assuming 1ns for rise/fall time (let me know if you want a specific time for your design), We should need at least 2500V/us SR. ADA4857-1would be a good choice.
        

         
        

        In Figure 25 of the DS, you will see that the large signal transient response for +/-5V rising and falling is steep. This looks like a good choice for your requirement.
        

        Regards,
        

        Kristine
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Mar 16, 2022 8:55 AM
            
            
												
						in reply to kristinehoffman
					
									
          
	
          

		
		
          
					
          I reckon that I did not specify the waveform - sorry for that!
          

          ADA4857-1 looks really nice, thanks a lot!
          

          I now also learned that I can filter the list by feedback type Slight smile
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

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