Need help with Colpits

[pkg]

Hi,

I am supposed to design a 2Ghz colpits oscillator using any effective
non-linear element..ie MESFET,BJT,JFETs, HBT etc

Can anyone guide me on the biasing circuit that one would need for the
Colpits to run at 2Ghz. Most of the circuits i used earlier involved
JFET or BJT's. But none of them work properly beyond a few Mhzs.

Any kind of help will be deeply appreciated.

Thanking you,

Pratik

 

[Jim Thompson]

On 6 Aug 2005 08:41:15 -0700, "pkg" <pratikg@gmail.com> wrote:

Hi,

I am supposed to design a 2Ghz colpits oscillator using any effective
non-linear element..ie MESFET,BJT,JFETs, HBT etc

Can anyone guide me on the biasing circuit that one would need for the
Colpits to run at 2Ghz. Most of the circuits i used earlier involved
JFET or BJT's. But none of them work properly beyond a few Mhzs.

Any kind of help will be deeply appreciated.

Thanking you,

Pratik

Try using one of those ceramic transmission lines that are shorted on
one end.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Tom LeMense]

Remember, your oscillator only needs a modest amount of gain (ideally 1.0,
but in practice slightly more) at your intended operating frequency - and I
can tell you from personal experience that it's very 'possible' to use a BJT
for a 2 GHz oscillator. The "common base" colpitts is my favorite circuit -
use a network tuned to 2 GHz to form an AC ground on the base, and use a
capacitive divider to couple some of the output (collector) back to the
input (emitter). You can start with a DC bias that sets I(C) and V(CE) to
whatever the datasheet uses for the "typical" operating point, then vary
from there as required. I'd recommend a transistor with Ft maybe 1.5 ~ 3x
your intended operating frequency; i.e. use a 3 to 6 GHz Ft transistor. The
higher the Ft, the more harmonics you'll have to contend with.

You will need to pay attention to the loading on the output though, the CB
configuration ends up with a high output Z - a buffer stage is advisable to
avoid "pulling", sometimes you can get away with very light coupling to the
output.

I think I used an MRF901 'back in the day' to make 2.54GHz oscillators for
field disturbance perimeter alarm sensors.

Good luck!

TJL




"Jim Thompson" <thegreatone@example.com> wrote in message
news:a0n9f1put8jrin355501jj8oei306ha605@4ax.com...

On 6 Aug 2005 08:41:15 -0700, "pkg" <pratikg@gmail.com> wrote:

Hi,

I am supposed to design a 2Ghz colpits oscillator using any effective
non-linear element..ie MESFET,BJT,JFETs, HBT etc

Can anyone guide me on the biasing circuit that one would need for the
Colpits to run at 2Ghz. Most of the circuits i used earlier involved
JFET or BJT's. But none of them work properly beyond a few Mhzs.

Any kind of help will be deeply appreciated.

Thanking you,

Pratik

Try using one of those ceramic transmission lines that are shorted on
one end.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.