Service Manuals, User Guides, Schematic Diagrams or docs for : Stanford Research Systems www.thinksrs.com-LDC Note 6 Modulation Input Divider

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Dividers for LDC500/501/LDC502 Modulation Input
                                                                                                           Rev B. Revised Oct 2012


 

 




                                                                                                        

                                                                 

                                    Figure 1   Balanced divider for LDC501 modulation input 

                                                                 

                                                                 

 

   There is no internal way to reduce the Modulate                     Circuit  shown  above  will  reduce  modulate  input 
sensitivity  on  the  LDC500,  LDC501  and  LDC502.                 sensitivity  100x,  to  0.25  mA/V  for  low  range  of 
This has to be done externally.                                     LDC501 and 0.5mA/V for its high range. 

   There  is  a  straight  forward  way  for  the  user  to             It  is  important  to  keep  R2  and  R3  matched  to 
reduce the gain on the Modulate input, and that is to               preserve the CommonMode Rejection performance 
build a simple voltage divider to place in series with              of  the  LDC501.  Do  NOT  simply  connect  the  outer 
the  input.  The  only  (important)  caveat  is  that  this         shell from J1 to J2. 
must  be  a  BALANCED  divider,  otherwise  the 
commonmode  rejection  performance  of  the                             Since the LDC500's modulation input impedance 
LDC501 will be completely ruined.                                   is about 2k, R1 should be kept below 50 ohms to 
                                                                    ensure gain accuracy. 
   Figure  1  shows  a  sketch  of  a  circuit  that  will 
reduce  the  modulate  sensitivity  100fold;  it  is 
straightforward to modify it from there as needed. 

 




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