What does it mean that output buffer of VCO is capable of driving 50 ohm load?

[eric0825]

i have studied some IEEE papers that says "the output buffer is capable of driving 50Ω load", does that means the output impedance of the buffer must be matched to 50Ω? or some other meaning?

 

[jfyan]

Re: Output buffer of VCO

i have studied some IEEE papers that says "the output buffer is capable of driving 50Ω load", does that means the output impedance of the buffer must be matched to 50Ω? or some other meaning?

hi, i think you are right.
generally, the output buffer is designed to drive some offchip transmission lines,which has a characteristic impedance Z0=50ohm.
good luck.
jeff.yan

 

[haytham]

Re: Output buffer of VCO

Hi
It means the load at the outbuf is 50 ohm.

Thanks

 

[tiger_ads]

Re: Output buffer of VCO

to eric0825
hi man , i am studying the output buffer of VCO, could u give me some reference paper!

thanks very much!

 

[eric0825]

Re: Output buffer of VCO

Source follower is the most frequently used topology, i've seen some modified edtion of source follower such as bias-T structure. The following is the reference:

N. H. W. Fong, J. O. Plouchart, N. Zamdmer, D. Liu, L. F. Wagner, C. Plett, and N. G. Tarr, "A 1-V 3.8-5.7-GHz Wide-Band VCO With Differentially Tuned Accumulation MOS Varactors for Comon-Mode Noise Rejection in CMOS SOI Technology", IEEE Trans. on Microwave Theory and Techniques, vol. 51(8), pp. 1952-1959, Aug. 2003.

I've heard that open-drain could also be used as output buffer, but i've not find any reference mentioned about it.

 

[dingjingfeng]

Re: Output buffer of VCO

the Output buffer is only used as driver to generate enough current to drive the off-chip 50 ohm .

usually the off-chip transmission line is 50 ohm which is the same as the load resisitor.

so you can simulate it as a 50 ohm load directly.