528MHz clock level conversion

RobJ · 2004-12-30T22:14:24+00:00

I need to amplify a low-level 528MHz clock to an LVCMOS-level compatible (i.e., 3.3V logic) single-ended clock. I have some control over the low-level clock, but assume it's a 400mVpp sine wave. It is generated by a Silicon Labs Si4133 synthesizer (IF output).There are no LVTTL/LVCMOS buffers out there that can handle anywhere near 528MHz. I can get almost to the level I need using wideband transformers from Mini-Circuits, but that causes large impedance changes across the transformers and I still barely end up with 2Vpp. I would prefer an active buffer using an Op Amp or transistor. The sine wave shape is not important (i.e., a square wave output is fine), but I do need to preserve the duty cycle as much as possible and minimize jitter. The system is nominally 50 Ohms (FR4 PCB traces) and the 3.3V clock load is a CMOS input buffer on an IC.Any suggestions would be appreciated.Rob

Dec 30, 2004 40 Replies

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Hi Rob:

That was a Virtex 2, two 15-bit channels interleaved to get the 1200MHz data rate, 600MHz "clock" rate. ISTR the latest wheeze is the "Rocket IO" stuff. I believe there's also some fast hardware for doing PCI Express arriving real soon now (tm).

John Larkin mentioned a requirement for 3V+ swings, I missed that. In an earlier post he also mentioned using an ECL driver - that can work _very_ well. It can be advantageous to use differential signals if you need to transmit any distance across your board (single ended can give you serious spur problems). If you use a beefy driver, and use, say, two 25-ohm or even less drive lines with a balun right next to your load, that should give a decent swing.

John mentioned the ERA family from MiniCircuits, I've had occasion to use some Watkins Johnson parts (AH11, AH101 etc) see:

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Look at the power dissipation, these puppies need decent thermals, and WJ have paid lots of attention to this.

Regards Ian