# switch for 1MHZ sine wave

I am trying to build a switch that can cut by control the sine wave V1
From the load R1. The main problem is that we have a parasitic capacitor between the drain and source So in high frequency this parasitic capacitor is act as bypass and I get a signal also when V2 = 0.

1. I can't use a really as I need to switch I in 100HZ.

2. SSR - solid-state relay is also not good for that from the seam parasitic capacitor .

Any idea will be helpful

Thanks Aharon.

simulate this circuit – Schematic created using CircuitLab

simulate this circuit

## 1 Answer

I'd consider using two switches - one in series to the load resistor from the source and then another across the load resistor. When one switch is activated the other one is off and vice versa.

• Or - assuming you're not allowed to short out the load ... 3 switches in a "T" network. Open the top two, and close the third to ground the common node. – Brian Drummond Jan 10 '16 at 13:52
• Hi Andy Sorry but see my update. Now to be clear I need to switch between sine wave and DC voltage on the seam load. For example 10ms sine wave then 5ms DC voltage . How can I prevent the high frequency parasitic capacitor ? – Aharon Jan 10 '16 at 14:00
• Put a 1uF capacitor in series with the shunting switch or modify it like Brian says so there are two series switches and a shunt switch in the middle. Anyway, if the DC "switch" has say 10 ohm on resistance and the other switch has 10pF capacitance the attenuation is still going to be significant circa 64 dB. How much AC attenuation do you need? – Andy aka Jan 10 '16 at 14:14
• @user96653 You said "So in high frequency this parasitic capacitor is act as bypass and I get a signal also when V2 = 0" - how can that be possible because V2 is THE sinewave signal and if V2 is zero you CANNOT get a signal. – Andy aka Jan 10 '16 at 14:19
• hmm..........Andi please see that V2 is the sine wave generator while V1 is controling the switch. – Aharon Jan 10 '16 at 14:27