Help with replacing mosfet with faster speed

[globalone]

I am building a fast switch driver circuit . Switching speeds are similar to the bipolar design.

The circuit provides 35nSec rise and fall times. This circuit will turn the switch on and off within 50nSec.

My target is to have faster speed for Turn-On/Turn-Off . 35nSec would be okay for the T-On/T-OFF , but I want to reach between 15nSec ~ 30nSec.

Do you think that BSS84DW (http://www.diodes.com/datasheets/ds30204.pdf) can be replaced with NDC7003P or NDS9948 ?.

What speed would i reach If I am going to use NDC7003P or NDS9948 ?.
http://www.fairchildsemi.com/ds/ND/NDC7003P.pdf
http://www.fairchildsemi.com/ds/ND/NDS9948.pdf

Are you familiar with (DUAL P-CHANNEL ENHANCEMENT MODE MOSFET). I have a working circuit that accept a logic input (0V/+5V) to bias a switch VC1 & VC2 (0V/-40V).

I had to use BSS84DW (http://www.diodes.com/datasheets/ds30204.pdf) , but the circuit provide a switching speed on and off within 50nSec and rise/fall 35nSec.


I have already found a replacement to BSS84DW with NDC7003P (http://www.fairchildsemi.com/ds/ND/NDC7003P.pdf) which should be faster , but I am not sure if it will use the same resistors , capacitors etc..

I want to know what should I get a Turn-OFF/Turn-ON speed if I am going to use the new PowerTrench MOSFET (NDC7003P) ?.

Please see the Driver circuit of the spdt switch that i am integrating into the switch.
The typical switch Ton/Toff speed is less than 15nSec but their rdriver has Ton/Toff 50nSec and Rise/Fall 35nSec. I thought of tuning the circuit to get a faster Ton/Toff.

Regarding the resistors R3A , R3B .. Should these resistors limit the current that should be passing to the Switch Voltage Control Lines 1 , 2 ?.

I got mentioned that .. In order to prevent negative voltage from appearing at the output of the inverters, the negative voltage applied to the level shifters must also equal the positive supply voltage. Once +/-5V is set on the circuit, the negative switch bias V- can be set anywhere in the -10 V to -40V range.

http://obrazki.elektroda.pl/3646151600_1371494410.png

The maximum rating of the control current at the switch is between -1 to 7.8 mA.

What do you suggest a value of the resistors at the circuit should be ?.
The link to the switch http://www.triquint.com/products/p/TGS2351 .

I really appreciate your recommendation


Ghassan

[pebe]

I am building a fast switch driver circuit . Switching speeds are similar to the bipolar design.

The circuit provides 35nSec rise and fall times. This circuit will turn the switch on and off within 50nSec.

My target is to have faster speed for Turn-On/Turn-Off . 35nSec would be okay for the T-On/T-OFF , but I want to reach between 15nSec ~ 30nSec.

The on and off times would be affected by propagation delays through components, and stray capacities.
It would not be possible to make valid suggestions without seeing your circuit.

[globalone]

I am building a fast switch driver circuit . Switching speeds are similar to the bipolar design.

The circuit provides 35nSec rise and fall times. This circuit will turn the switch on and off within 50nSec.

My target is to have faster speed for Turn-On/Turn-Off . 35nSec would be okay for the T-On/T-OFF , but I want to reach between 15nSec ~ 30nSec.

The on and off times would be affected by propagation delays through components, and stray capacities.
It would not be possible to make valid suggestions without seeing your circuit.

Thanks for your information.

I already added a link to my circuit (http://obrazki.elektroda.pl/3646151600_1371494410.png)

Can you see this circuit . Im sorry i couldnt attach files because there is no link on this forum to attach so i attached the circuit at external website.

I really appreciate your help

[globalone]

Hello,

I have already put my circuit but its not attached into this forum. I have attached it externally.

Please see my circuit
http://obrazki.elektroda.pl/3646151600_1371494410.png

Are you able to see my circuit ?.

I really appreciate your hellp

[globalone]

Hello,

I am not sure what is happening with my posts. I have replied to you 2 times but I didn't see my replies.

I have addd http://obrazki.elektroda.pl/3646151600_1371494410.png . That is the circuit that I have drawn.

I am afraid of the time to turn on the switch and off.
The company who owns this switch TGS2351 has mentioned that the maximum absolute control current for the switch is between -1 to 7.8 mA.

I want someone to explain the circuit because the 18K resiatance at Drain of the mosfet slows the time but limit the current . How can I tune this driver circuit to turn on and off the switch within 35nSec or faster.

The company said this circuit should turn on and off the switch within 50nSec. How did they measure the details ?.

What is the delay of the situation of the drawn circuit between VC1 to VC1 in a situation of turning off and On?.

[pebe]

The company said this circuit should turn on and off the switch within 50nSec. How did they measure the details ?

They probably used a dual beam scope to measure the delay between the waveforms at the input and VC1 output.

What is the delay of the situation of the drawn circuit between VC1 to VC1 in a situation of turning off and On?

I assume you mean between VC1 and VC2. The difference in delay times between the two outputs is the propagation time through the 2A-2Y inverter. Nominally about 2.5nS

The 1K resistors R2A&B are to pull the gate voltage (pin5) down to -5V when the inverter output 1Y goes low and D1B cuts off. The input capacity at pin5 is about 60pF and that has to be charged up by the 1K.

A better way would be to put a 500nF capacitor in parallel with each of D1A and D1B. R2A&B could then be made larger so decreasing the load on the inverters.

I want someone to explain the circuit because the 18K resistance at Drain of the mosfet slows the time but limit the current . How can I tune this driver circuit to turn on and off the switch within 35nSec or faster.

The two 18K resistors are drain loads necessary to produce an output voltage at the drains. Their value will not affect the turn-on time but will affect the turn-off time because the internal drain capacity has to charge from 0V to -40V through the resistor.

To answer you earlier question about replacing the BSS**** FET with an NDC**** one.
It is not possible to directly compare switching times from the data sheets because they do not compare like with like. One shows On/Off times, while the other shows additional rise times.