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HMC346ALC3B Production
The HMC346ALC3B is an absorptive Voltage Variable Attenuator (VVA) in a leadless “Pb free” RoHS compliant SMT mount ceramic package operating from...
Datasheet
HMC346ALC3B on Analog.com

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HMC346ALC3B application

		
	
				

			

									
					    PicardL
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Mar 9, 2021 
				
			
			
		

		
		                    	    

        	    
Thread Summary

                The user is experiencing issues with continuous attenuation control using the HMC346ALC3B voltage-variable attenuator with an AD8675 op-amp. The final answer suggests verifying if V1 is being varied from 0V to -5V and checking the part's functionality by controlling V1 and V2 separately with two power supplies, as per the 'Relative Attenuation vs. Control Voltage @ 10 GHz' figure in the datasheet. The accompanying answer clarifies the relationship between V1, V2, and I, noting that I maintains impedance match while V1 and V2 control attenuation.
                        	    

                
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I have been trying to use the HMC346ALC3B voltage-variable attenuator as part of a laser intensity control circuit, and I am having some trouble with the external op-amp control circuit. 


I have wired an external op-amp (AD8675) control circuit together with the HMC346ALC3B eval board, exactly as shown in the datasheet for the attenuator: https://www.analog.com/media/en/technical-documentation/data-sheets/hmc346alc3b.pdf


I am using an external DC power supply for the control voltage. However, I do not see continuously tunable attenuation, but rather 0 attenuation for 0 - 4V control signal and a sudden change to 20 dB attenuation above 4V.


Hoping to get some suggestions about the cause of this problem, or any kind of more detailed explanation / application note for the HMC346ALC3B which would allow me to design a new circuit. Currently it's not very clear to me from the datasheet alone what exactly the V1, V2 and I inputs should be.

			

			
									
		                             
                        

    

                                            
                 hmc346alc3b
                
                                                    
                 Voltage Variable Attenuators
                
                                                    
                 rf & microwave
                
                                                    
                 attenuators
                
                                                    
                 attenuator
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			


				
	









	
    
	

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Mar 16, 2021 2:04 PM
            
            
						
			            		
    
		
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    1. When you wired an external op-amp with HMC346A as indicated in the datasheet, you only need to vary the voltage of V1 (from 0V to -5V). V2 will be complimentarily changed by the op-amp and I maintains the impedance match while attenuation is varied. Is this what you have been doing so far and still observe a sudden change of attenuation?
    

    2. Since you have the HMC346A eval board, you can also check if the part is still functioning by not using the external op-amp first. You can find two power supplies and control V1 and V2 separately. Please refer to the figure "Relative Attenuation vs. Control Voltage @ 10 GHz" in the datasheet. You can try to check several combination points of V1 and V2, and to see if you can achieve the expected attenuation levels.
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
				
				
				
		
		
    
			
		
    
	
    

    

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                on May 26, 2022 4:16 PM
            
            
												
						in reply to zwang
					
										
			            		
    
		
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    If i want to control the v1 and v2 using external voltage, What is the relation between V1, V2 and I? Do i need to measure this on my own?
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

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