LTC6404 input circuit

Question

Dear Sir or Madam 
 I am implementing my design with LTC6404-2 , and not sure if the circuits will work well , especially about the input part , where switches are inserted between the input resistors (R1,R2) and feedback resistors(R5 , R6) , Besides , are there any issues if I place the R1 ,R2 far away from LTC6404-2 input pins respectively in my layout design ?

Is the circuit OK? 
 Thank you in advance for your advice. 
 
 sincerely 
 Best regards 
 Anglic

Hooman · Accepted Answer

Hi Anglic, 
 I posted a response to your other post about using LTC6404-1 at lower than 1V/V gain here: 
 https://ez.analog.com/amplifiers/f/q-a/122606/questions-about-ltc6404-1/364681#364681 
 In general you'd want to minimize all trace lengths with a device as fast as LTC6404-1. You probably have to experiment with it on a prototype board to make sure though. 
 I see the plot you've noted about cap across RF to mitigate peaking. That's certainly a valid technique: 
 
 You had asked if LTC6404-1 can be used to drive AD9650 ADC. 
 From AD9650 datasheet: 
 
 Analog input: 2.7Vpp (Vref = 1.35V) 
 Input CM voltage: 0.9V 
 
 From LTspice, these conditions look doable as shown below: 
 
 With some drivers, approaching the ~0.2V from ground may be troublesome. I've seen designs where the FDA is used with its V- supply pin powered from a slightly negative supply such as -0.7V to alleviate the swing so close to the V- rail. But, if LTspice can be trusted (which I tend to do), first order seems like a doable proposition (unless distortion terms become too large with swing so close to the V- rail). 
 Here is the LTspice file for your review: 
 2620.LTC6404-1 AD9650 driver EZ 2_26_20.asc 
 Regards, 
 Hooman)

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LTC6404 input circuit

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