How to make FET invert the drain?

Thread Starter

johnyradio

Joined Oct 26, 2012
254
I have two square-wave signals. I'm using one to turn on the other. Need to open the gate when the slower signal goes low. Using N-channel works well (top trace is output):

http://tinyurl.com/y8ddbt7a

However, i'd like to square-wave at the drain to be inverted at the output. Is there a way to achieve that without adding another transistor?

Changing to a P-channel doesn't help. Exchanging the clocks doesn't help.
 
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Thread Starter

johnyradio

Joined Oct 26, 2012
254
thx for running that! But, i want to get output when the low-freq goes to ground. In yours, we get output when the low-freq goes high.
 

AlbertHall

Joined Jun 4, 2014
10,017
Connect both signals to the gate via diodes, cathode to the gate, and add a resistor from gate to ground (10k?). Connect the drain resistor to a power supply.
 

crutschow

Joined Mar 14, 2008
25,114
:rolleyes::rolleyes:
Connect both signals to the gate via diodes, cathode to the gate, and add a resistor from gate to ground (10k?). Connect the drain resistor to a power supply.
Do you mean anode to gate so that the diodes act as an AND gate?
Also the 10k resistor from gate to V+?

LTspice simulation of that below.

Possible disadvantage is that the gated "off" output voltage is +5V, not 0V.

upload_2018-10-6_17-58-49.png
 

Bordodynov

Joined May 20, 2015
2,624
Hi.
The first thing I want to say is that the original (first) diagram is not correct (absurd).When 15 Hz has a high level the output will be zero.Nevertheless, I propose a scheme in which the output is inverted (inverse).
See
cir1.png
 

Attachments

AlbertHall

Joined Jun 4, 2014
10,017
Do you mean anode to gate so that the diodes act as an AND gate?
Also the 10k resistor from gate to V+?
Errr...Ummm...
From the original post looking at the circuit, When the gating signal is high the output will be low, but in the waveforms shown when the gating signal is high the output is high.

To match the circuit the diodes need to be cathode to gate (OR gate), to match the waveforms the diodes need to be anode to gate (AND gate).
 

Thread Starter

johnyradio

Joined Oct 26, 2012
254
thx for replies, many thx for time y'all spent coming up with solutions!

Apologies but i found a workaround for my needs, so i don't need to do the topic of this thread for now.

feel free to keep discussing :)
 
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