Jan 20, 2011 #1 Z zhangm79 Member level 1 Joined Apr 5, 2006 Messages 38 Helped 1 Reputation 2 Reaction score 0 Trophy points 1,286 Activity points 1,491 Hello, i am designing LNA using FET transistor. But when connnect -Vgg with gate of FET, the voltage changed.the measured Vg is not -V as expected. source of FET connected to ground. Is it normal or something wrong?How to debug real bias? thanks.
Hello, i am designing LNA using FET transistor. But when connnect -Vgg with gate of FET, the voltage changed.the measured Vg is not -V as expected. source of FET connected to ground. Is it normal or something wrong?How to debug real bias? thanks.
Jan 20, 2011 #2 J jayce3390 Full Member level 6 Joined May 22, 2007 Messages 351 Helped 29 Reputation 58 Reaction score 21 Trophy points 1,298 Activity points 3,287 Hi, Post the biasing circuit topology. Did you put a resistor in it? What is the supply voltage? And gate voltage? Some RF power is maybe going through the bias network...
Hi, Post the biasing circuit topology. Did you put a resistor in it? What is the supply voltage? And gate voltage? Some RF power is maybe going through the bias network...
Jan 20, 2011 #3 V vfone Advanced Member level 6 Joined Oct 10, 2001 Messages 5,709 Helped 1,616 Reputation 3,237 Reaction score 1,248 Trophy points 1,393 Activity points 36,250 It is possible your LNA to oscillate.
Jan 20, 2011 #4 B biff44 Advanced Member level 6 Joined Dec 24, 2004 Messages 5,047 Helped 1,376 Reputation 2,748 Reaction score 1,056 Trophy points 1,393 Location New England, USA Activity points 37,908 Yes, I was thinking oscillation too. How are you measuring the gate voltage. You can not just attach a DVM probe to the gate!
Yes, I was thinking oscillation too. How are you measuring the gate voltage. You can not just attach a DVM probe to the gate!
Jan 20, 2011 #5 Z zhangm79 Member level 1 Joined Apr 5, 2006 Messages 38 Helped 1 Reputation 2 Reaction score 0 Trophy points 1,286 Activity points 1,491 thanks, guys. bias should be -0.5v on the gate, 3V on the drain. Biff44, how to measure gate voltage? ---------- Post added at 17:20 ---------- Previous post was at 17:20 ---------- 50ohms resister in bias of gate and drain.
thanks, guys. bias should be -0.5v on the gate, 3V on the drain. Biff44, how to measure gate voltage? ---------- Post added at 17:20 ---------- Previous post was at 17:20 ---------- 50ohms resister in bias of gate and drain.
Jan 20, 2011 #6 tony_lth Advanced Member level 5 Joined Jul 28, 2010 Messages 2,088 Helped 377 Reputation 756 Reaction score 368 Trophy points 1,363 Location Beijing Activity points 12,641 Bias resistor should more than 300R. Bias voltage resistors is almost compared to resistor of the transistor.
Bias resistor should more than 300R. Bias voltage resistors is almost compared to resistor of the transistor.