Maximum Ic of a transistor in ADS Harmonic Balance

Hi,

I'm designing an oscillator using ADS. The transistor I use has a maximum Ic of 30 mA. I placed an ammeter between collector and the rest of the circuit and I'm simulating the circuit using Harmonic Balance. I got separate current values for each harmonic:

harmindex / mag(Ic.i)
0 / 27 mA
1 / 17 mA
2 / 5 mA
...and so on

And now the question - is the maximum Ic exceeded? Should I look only at the DC component or sum all harmonics (which gives much more than 30 mA)?

I placed another ammeter between the DC supply and the circuit and I got:
0 / 27 mA
1 / 2 mA
2 / 0.03 mA
...

In my opinion the maximum Ic is exceeded - there's a constant 27 mA current flowing through the collector (even if the circuit isn't oscillating) and there's additional current from the subsequent harmonics (that goes to/from the oscillator output).

But I found some designs on the net (oscillators, amplifiers, etc.), where the Ic is measured only during DC simulation and is compared to transistor's maximum Ic. That suggested that only the DC current is important.

Which one is true?

Best regards,

Piotr

paszczakojad said:

Should I look only at the DC component or sum all harmonics (which gives much more than 30 mA)?

Click to expand...

Both are wrong.

You have to see ts(Ic.i).
And also you have to see Pc=ts(Ic.i)*ts(Vce).

pancho_hideboo said:

paszczakojad said:

Should I look only at the DC component or sum all harmonics (which gives much more than 30 mA)?

Click to expand...

Both are wrong.

You have to see ts(Ic.i).
And also you have to see Pc=ts(Ic.i)*ts(Vce).

Click to expand...

That looks very similar - maximum of ts(Ic.i) is 50 mA while sum(mag(Ic.i)) is 51 mA (at the collector). The same is in case of supply current - 29 mA and 29 mA.

So the maximum current seems to be exceeded...

P.

You have to check Max[Ic(time)], Max[Vce(time)] and Max[Pc(time)].