I'm playing around in ngspice & trying to understand envelope detectors for ham radio.
I'm pumping 150Mhz into the circuit described below - I'm expecting it to go positive in proportion to amplitude + frequency. After a bit, it goes negative. Whats happening here?
Consider this circuit:
- 150Mhz 2V sine wave input, 50ohms impedance
- D1N4148 diode
- 100pF smoother capacitor
- 500k bleed/load resistance
Spice input I'm using / working on:
Detector CIRCUIT .model D1N4148 D (IS=0.1pA, RS=16 CJO=2pF TT=12N BV=100 IBV=0.1pA) v1 1 0 sin(0 2 150MEG) rSOURCE 2 1 50 d1 2 3 D1N4148 c1 3 0 100p rLOAD 3 0 500k .control tran 5us 50ms run write kek.raw v(3) quit .endc .end
Gives me this:
Note the negative sections.
How does a diode detector go negative like this? how do I stop it?