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LTC6253 Last Time Buy
The LTC6252/LTC6253/LTC6254 are single/dual/quad low power, high speed unity gain stable rail-to-rail input/output operational amplifiers. On only 3.5mA...
Datasheet
LTC6253 on Analog.com

LTC6254 Last Time Buy
The LTC6252/LTC6253/LTC6254 are single/dual/quad low power, high speed unity gain stable rail-to-rail input/output operational amplifiers. On only 3.5mA...
Datasheet
LTC6254 on Analog.com

LTC6252 Last Time Buy
The LTC6252/LTC6253/LTC6254 are single/dual/quad low power, high speed unity gain stable rail-to-rail input/output operational amplifiers. On only 3.5mA...
Datasheet
LTC6252 on Analog.com

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LTC6253 - GBP 720MHz, but gain of 10 = BW of ~35MHz??

		
	
				

			

									
					    QBort
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 14, 2019 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    Hello,
    

    I am trying to design a circuit to achieve a gain of 10 for input signals up to 50MHz. I have looked at LTC6253 as a possibility, since it has quite a large GBP of 720MHz. If my understanding is correct, for a gain of 10, it should handle up to 720/10 = 72MHz
    

    I have done a simulation on LTSpice, of non-inverting op-amp with a gain of 10 but it shows that the bandwidth would end up being around 35Mhz.... See screenshot below. 
    

    The datasheet recommends to use a capacitor in the feedback loop to compensate stray capacitances (C1 in my simulation). Through trial and error I have found this to be around 0.5pF.
    

    It seems there are other parameters I need to consider when selecting my op-amp for this application. Does anyone have any suggestions as to what causes a reduction in effective bandwidth vs what I would have expected from the GBP?
    

     #
    

    

    Thanks!
    

    

    Qbort
    
			
    
			
									
		                             
                        

    
    
                                            
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Mar 14, 2019 12:15 PM
            
            
						
			            		
      
		
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      Hi Qbort:  The 2GHz spec is the gain-bandwidth-product.  It is the product of gain and frequency at a relatively low frequency.   In this case, the GBW product was specified at 10MHz, and indicates a typical gain of 200 (46dB) there. 
      

      In a gain of 10, consulting the Gain-Phase curve, you should expect a bandwidth of about 85MHz (on a 5V supply, less on a 3V supply).  I suspect the problem is that your resistor values are too high, so you are up against the feedback pole and necessary compensation.  I suggest you try again with resistor values of 200:450 instead of the 1k:9k, and you should be able to get significantly higher bandwidth.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Mar 14, 2019 3:27 PM
            
            
												
						in reply to ADIApproved
					
										
			            		
        
		
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        Dear GlenBrisebois,
        

        Thank you for your reply.
        

        I have tried as you suggested of lowering the resistor values (I assume you meant 50:450, for a gain of 10), but saw no noticeable difference. I have even removed the compensation capacitor but it just means the output overshoots (See screenshot below), and maybe marginal increase in bandwidth to 45MHz, but I would expect a bandwidth of at least 72MHz if the GBP is 720MHz and the gain is 10?
        

        Also, just to point out, I think you might be getting confused with a different part? There is no mention of 2GHz in the datasheet of the LTC6253. The GBP is 720MHz as shown on the front page (see extract below).
        

        

         
        

         
        

        

        Thanks again,
        

        Qbort.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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