I'm already back with another ring oscillator ! and @Tim will love this one even more.
The precedent one gave me some headaches due to the bad PCB design, I used a single-sided board and couldn't solder anything on the other side... ma que stupido !
I de-soldered the transistors and made a new board with more headroom. Aaaaaand...
13.30MHz @ 2.42V / 30mA => that's 4.2ns per inverter !
The new parameters are not far from the previous one :
Rb = 150 Ohms, Rc = 470 Ohms
The change of Rb seems to have helped a bit : I now see the collector voltage saturated and not reaching Vcc (between 0.15 and 1.25V). Vb ranges from 0.18V to 0.9V => I'm now near the levels defined by CDC !
Here is the waveform at the base : the 2N2369 is driven hard at 800mV ! Discharging it however seems to take some time...
The other change is the ample decoupling, 6×100nF + 3×10nF, I don't know if it helps but you're never too safe with that because later, I might unexpectedly scramble the local CB channels ;-)
Yet I don't see how/why I gained 30% speed with the same transistors (I replaced one by error) and almost the same resistors (ok the base resistor has lost 25% of its value... but it's worth it right ?)
Did I mistake a resistor somewhere ? Was one of the transistors "too slow" ? Is there a wrong resistor value in the first RingO ?
Something else is interesting : I'm now at 30mA but the last "record" was at held at 50mA so something serious is going on here ! Efficiency has jumped too !
The signal falls in about 5ns on the 200MHz scope, which is close to the limits. There is some overshoot, very likely caused by the ground clip and the limited BW of the whole system.
Another good sign is that the falling edge (at the collector) is now the fast one, in 5ns :-) (we were puzzled that the rising edge was the fast one on the other board, might have been mistaken for the base ? nah...)
The rising edge takes about 12 ns to completely reach 1.1V and this will get only longer with more loading. But in 8ns, 1V is reached.
At 2.5V and 470 ohms shorted in DC to 0V, the collector current is drawing 5mA (approx.)
Add to this the other current source (the base capacitance and the transistor might have 10mA transients... So once again it's in line with the CDC specs :-)
The base current is defined by (Vc - Vb) / Rb = (1.2 - 0.85) / 150 => Ib = 2.3mA (at 2.5V, during DC ON) => in line with the expected values :-)
The circuit alternates between 5mA and 2.5mA, this averages to 3.7mA/9.3mW per inverter (FO1).
The delay :
This plot is from the base and collector of the same transistor, so we see the latency of the signal : about 5ns between the middle point of the rising edge on the base and the middle point of the falling edge of the collector. It takes about 8ns from the start of the base's rising edge to the end of the collector's falling edge...
The reverse however takes more time, due to RC loading.
The V/F curve :
V mA MHz 1 6 8.292 1.1 8 9.191 1.2 10 9.942 1.3 11 10.576 1.4 13 11.140 1.5 15 11.609 1.6 16 12.001 1.7 18 12.344 1.8 19 12.636 1.9 21 12.867 2 23 13.053 2.1 24 13.182 2.2 26 13.286 2.3 28 13.343 2.4 30 13.364 2.5 31 13.354 2.6 32 13.317 2.7 34 13.253 2.8 36 13.170 2.9 38 13.068 3 40 12.952 3.1 41 12.826 3.2 42 12.689 3.3 44 12.552 3.4 46 12.408 3.5 48 12.253 3.6 49 12.097 3.7 51 11.938 3.8 53 11.729 3.9 55 11.580 4 56 11.426
Clearly : something important has happened :
set xlabel 'V' set ylabel 'MHz' set y2label 'mA' set xr [1:4] set yr [6:18] set y2r [0:120] set ytics 1 set y2tics 10 set key right bottom plot "27pf.dat" using 1:3 title "v.1 27pF Frequency in MHz" w points pt 7, \ "27pf.dat" using 1:2 axes x1y2 title "v.1 27pF total current in mA" w points pt 7, \ "ringo9_2_sans.txt" using 1:3 title "v.2 sans cap Frequency in MHz" w lines, \ "ringo9_2_sans.txt" using 1:2 axes x1y2 title "V.2 sans cap current in mA" w lines
The behaviour is temperature-sensitive...
The PSU's ammeter is really wiggly !
Efficiency at peak (2.5V) :
- v1+27pf : 54mA 16.65MHz 135mW => 8.108mW/MHz
- v2 : 31mA 13.354MHz 77.5mW => 5.8mW/MHz
Something really interesting is happening since v1 ! Is it thanks to all the decoupling ?