-1
\$\begingroup\$

Two symbols are the same sample and hold,so Theoretically their ouput should be the same,but as we see,when i connect it with a comparator,the output of sample and hold totally change.

Why?How do i improve this?add a unit gain amp at the output of sample and hold?By the way,the red one seems read the comparator clock.

duty cycle of clock for sample and hold:85%

duty cycle of clock for comparator:50%

enter image description here

\$\endgroup\$
  • \$\begingroup\$ int he simulation, put a load resistor on the blue output. see what happens. \$\endgroup\$ – jsotola Nov 3 '17 at 2:51
  • \$\begingroup\$ it changed,how do i modify it? \$\endgroup\$ – Shine Sun Nov 3 '17 at 3:50
  • \$\begingroup\$ Your own suggestion how to fix is appropriate. \$\endgroup\$ – Brian Drummond Nov 3 '17 at 10:28
1
\$\begingroup\$

The blue curve is an ideal scenario where there is no load where as the red waveform is more realistic as the gate capacitor of amplifier acts as load. Blue curve however is not achievable but it can be much better than red one.

The tweeks to improve output after sample and hold can be done:

  • Changing hold capacitor
  • Reducing Ron of Sample switch
  • Reduce input capacitance of amplifier
  • Use a dummy transistor after the sample switch to reduce the non-linearities

All this are provided in "Design of Analog CMOS circuits" by B.Razavi though only analysis.

| improve this answer | |
\$\endgroup\$
0
\$\begingroup\$

I have improve that by adding two buffer,which is two stage amp

enter image description here

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ This increases power by 2 times, if you are ok with it then looks good. \$\endgroup\$ – rsg1710 Nov 6 '17 at 14:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.