Hi,

I am looking for a transistor that I can use as a switch at a minimum frequency of 10 MHz.

So far, I haven’t been able to find a suitable component, and I would really appreciate your assistance or recommendations.

My circuit is intended to look like this:


Thank you very much for your help.

 

hi Toni,
what voltage levels, and required rise/fall times, also what is the load impedance?
E

 

How about 2N7002?, can handle for 10-20 MHz, but how about amp. Voltage and gate charge ratings?

 

 

The switching speeds of a MOSFET are dependent on how you drive the gate. Show us your entire test circuit if you want better help. Pretty much any modern MOSFET can switch at 10MHz with the right gate drive.

 

hi Toni,
what voltage levels, and required rise/fall times, also what is the load impedance?
E

Hi,

I want the transistor to conduct and pass a voltage of about 2.4V, and when the transistor is off there will be a pull-up resistor on the output to 5V.
In other words, I want to switch the output between 2.4V and 5V.
You can see the context in my post here:
https://forum.allaboutcircuits.com/threads/power-amplifier-switching-and-mute-circuit.209695/

Thank you very much

 

How about 2N7002?, can handle for 10-20 MHz, but how about amp. Voltage and gate charge ratings?

The switching speeds of a MOSFET are dependent on how you drive the gate. Show us your entire test circuit if you want better help. Pretty much any modern MOSFET can switch at 10MHz with the right gate drive.

Hi,
In this post I described everything in detail, but I didn’t receive a response there.
Thank you very much.

https://forum.allaboutcircuits.com/threads/power-amplifier-switching-and-mute-circuit.209695/

 

From the other post.
What is the load like at "Vs_NEG"? Low impedance or high impedance? Tell us what you are driving.
What is the voltage at "ON?OFF"? Who is driving this?
What supplies do you have? +V, -V, V_s, and 5V.
There are so many unknowns we cannot comment much.

 

From the other post.
What is the load like at "Vs_NEG"? Low impedance or high impedance? Tell us what you are driving.
What is the voltage at "ON?OFF"? Who is driving this?
What supplies do you have? +V, -V, V_s, and 5V.
There are so many unknowns we cannot comment much.
View attachment 364040

Hi, you're right.
I am driving a power amplifier that has both a positive supply and a negative supply. I am focusing on the negative supply. The load I’m driving is high impedance.

The ON/OFF signal is a control signal from the microcontroller that drives the transistor. Basically, I just want to switch the transistor, but I’m not sure whether to drive it directly from the MCU or use a driver (or something else).

The supply v+ = 5V , v-=-5V, V_S is around ~2.4V

Thank you very much

 

V_S is around ~2.4V

Does V_S move, or is it fixed at about 2.4V.

 

Something like this one transistor level-shifter?
(LTspice sim below for a 10MHz input):

 

I thought about one transistor circuit but did not.

V1 is the output from the computers. I have it set to 0/3.3V but it could be almost anything. 0/5V
R1, R2 sets the slicing point. It is not set to 2.5V but could be set to half of 3.3V.
V2, V3 are the +/-5V supplies.
LT1711 compares the two input voltages.
Out swings from -5V to +5V.
Out2 swings from -5V to -2.5V as set by R3, R4.

The rise and fall time is in the order of 4nS. See attached SPICE file.

 

The rise and fall time is in the order of 4nS.

You won't get anywhere near that at out2 with typical stray circuit capacitances.

 

You won't get anywhere near that at out2 with typical stray circuit capacitances.

I believe both circuits have about 1k impedance. Maybe about the same speed driving a capacitor.

I like that you keep the transistor out of saturation. I have used grounded base amplifiers many time in video and RF amps. Good job.

 

I believe both circuits have about 1k impedance. Maybe about the same speed driving a capacitor.

So what might be the advantage of your circuit, given its greater complexity?

 

Does V_S move, or is it fixed at about 2.4V.

The voltage may vary because I am adjusting the operating point of the power amplifier.

 

So what might be the advantage of your circuit, given its greater complexity?

I all ready said:

Good job.

I said:

I like that you keep the transistor out of saturation.

I am not here to fight with you. Do you need another compliment?

given its greater complexity?

Why? I never got an answer if the input "V_S" voltage should control the output "VS_Neg" voltage. In you wonderfully simple and cleaver circuit there is a connection between the two voltages. In the first circuit with an op-amp there is also this connection.
I made a circuit where variations in V_S did not pass through to VS_Neg. It is on or off. (digital vs analog) Done to clean up noise from the computer.
---edited---
Sorry for being grumpy. I have not had coffee yet.

 

Sorry if sounded like I wanted a fight.

I didn't need an attaboy, just wanted to know what advantages your circuit had, since you posted it after mine.

Trust you enjoyed your coffee.

 

The voltage may vary because I am adjusting the operating point of the power amplifier.

You could change R3 to 500Ω and add a 1kΩ pot in series connected as a rheostat with my circuit to allow adjustment of the 2.4V level

Also the value of the input control voltage affects that level.
What is the voltage from the micro?

Would you want the circuit output voltage level to be controlled by the micro?

 

Something like this one transistor level-shifter?
(LTspice sim below for a 10MHz input):

View attachment 364045

Hey
The circuit looks very interesting. I’d be happy if you could elaborate a bit more on it and explain how it works. Does this circuit have a specific name that I can look up and read about ?
Additionally, if I don’t want the 2.4V level to be fixed — but instead adjustable — so I could set it to something like 2.5V, 2.2V, or 3V, how could I control that value?
Thank you


Thank you very much.