Analogworld
Member level 1
bottom plate sampling
Hi all,
To suppress the distortion of the sampling switches that needed to pass 500MHz bandwidth signal, some techniques has been done it before:
1) Increase the transistor size to reduce the on resistance, so that the distortion is suppressed. However, a big transistor also makes a bit parasitic capacitor. I tried this technique, the transmission gate transistors size turns out to be W/L=2700! to keep the THD as low as 0.1% at 500MHz. This size is ridiculous.
2) Bootstrapping technique, which keep the Vgs of the transistor constant when the switch turns on. Compare to technique 1), it only requires W/L=300 to keep the THD as low as 0.001%. However, this technique requires complicated layout. I been told that the guy who first pulish this technique spent one year on the layout!
3) Peoples saying that connect the source of the p-type transimission switches to the bulk(body) when the switch is on (on-resistance reduced), then connect it back to vdd when it is off (off-resistance increased). However, the distortion performance does not improved when I do the simulation in spice.
Does anyone have any advice regarding to this topic? Any suggestion would be greatly appreciated.
Hi all,
To suppress the distortion of the sampling switches that needed to pass 500MHz bandwidth signal, some techniques has been done it before:
1) Increase the transistor size to reduce the on resistance, so that the distortion is suppressed. However, a big transistor also makes a bit parasitic capacitor. I tried this technique, the transmission gate transistors size turns out to be W/L=2700! to keep the THD as low as 0.1% at 500MHz. This size is ridiculous.
2) Bootstrapping technique, which keep the Vgs of the transistor constant when the switch turns on. Compare to technique 1), it only requires W/L=300 to keep the THD as low as 0.001%. However, this technique requires complicated layout. I been told that the guy who first pulish this technique spent one year on the layout!
3) Peoples saying that connect the source of the p-type transimission switches to the bulk(body) when the switch is on (on-resistance reduced), then connect it back to vdd when it is off (off-resistance increased). However, the distortion performance does not improved when I do the simulation in spice.
Does anyone have any advice regarding to this topic? Any suggestion would be greatly appreciated.