Hello again.
I have a question on a new analog devices reference design. This circuit employs transimpedance gain switching, which is what I am currently researching. They use the ADG633 CMOS switch to swap out the feedback network of the amplifier. I understand that the switch has an on resistance of about 50ohms, which in the feedback loop will add a 50ohm error to the gain. What I don't understand is how connecting another switch at the output of the device, nulls this error? This is demonstrated about 1/3 the way down the page:
http://www.analog.com/en/circuits-from-the-lab/CN0312/vc.html
Any clarity on this matter would be greatly appreciated!
I have a question on a new analog devices reference design. This circuit employs transimpedance gain switching, which is what I am currently researching. They use the ADG633 CMOS switch to swap out the feedback network of the amplifier. I understand that the switch has an on resistance of about 50ohms, which in the feedback loop will add a 50ohm error to the gain. What I don't understand is how connecting another switch at the output of the device, nulls this error? This is demonstrated about 1/3 the way down the page:
http://www.analog.com/en/circuits-from-the-lab/CN0312/vc.html
Any clarity on this matter would be greatly appreciated!