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Design >> RF Design >> Designing LC CMOS VCO (GSM900)
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Message started by shaanto on May 10^th, 2004, 10:55pm

Title: Designing LC CMOS VCO (GSM900)
Post by shaanto on May 10^th, 2004, 10:55pm

Hi all

I am designing a double cross-coupled LC CMOS VCO for GSM900. I am trying to figure out a way to determine the W/L ratios of the two pairs of cross-coupled PMOS and NMOS transistors. I would like to know what factors I would need to take into account while doing this. I did look a lot of papers presented but they all dealt with phase noise and design of the tank circuit. Are there any design equations to obtain the width and length..?

Any help would be greatly appreciated.

Title: Re: Designing LC CMOS VCO (GSM900)
Post by wccheng on May 15^th, 2004, 7:27pm

Dear Sir,

Actually, you could equate the circuit in the small signal analysis. You just need to make the gain of the transistor could compensate the total loss of the total parasitic resistance in the LC tank. The VCO could oscillate. Most of the VCO book will introduce this direct method to do it. The Phase Noise reduction is due to others factor. You could search some paper in the IEEE. I hope the reply could solve your problem. ;)

Best Regards,

wccheng