Gerhard Oops! I meant s12 not s21. Bruce

I've done a redesign of the distribution amplifier without transformers or other ferrite (apart of dc filters). This required 2 transistor chains in parallel or 96 mA at 24V / Channel. It runs quite hot but looks like it could work from KHz to 600 MHz+. Harmonics are down 40 dB at 250 MHz/13 dBm including SMPD signal generator and the 54846B scope digitizers. AF decoupling is in again as well as Bruce's base divider caps. http://www.hoffmann-hochfrequenz.de/downloads/IMG_0499__Q73.jpg I had quite a lot of stability problems in the last stage; it liked to oscillate at 1.5 to 3 GHz. I had to use 33R base stoppers for the pnp transistors and tried a week's evenings with Genesys to get rid of them to no avail. I even tried 0603 base decoupling caps right _through_ the board from the base pad to the ground plane 0.5mm / 20 mil away. There is still a lot to do optimizing the voltage drops per stage and characterizing that thing. Any idea of more harmless pnp wideband transistors with Ptot = 1W? Maybe I could run this with -24V and use more NPNs and the pnp only in the CC stage. The efficiency might be improved with a 10 uH choke from the final collectors to gnd. That could be accomplished without ferrite or at least with a large air gap. regards, Gerhard dk4xp

On Mon, 22 Sep 2008 01:01:31 +0200, you wrote: >after reading "A low noise 100 MHz distribution amplifier for precision metrology" >by M. Siccardi, S. Römisch, F. W. Walls, and A. De Marchi (NIST), >I have implemented a homebrew version of their design. > >Circuits, simulation & measurement data are contained in: I have done a new revision of the distribution amplifier. It has now 6 + 1 channels on a double EuroCard (usual VME bus size) http://www.bilder-hochladen.net/files/9hqp-5-jpg.html I got first silicon^W^W^W epoxy a few days ago, the board is not yet completely populated, but channel 1 works already as expected. I will characterize it after the easter holidays. The circuit is essentially the LT-spice circuit that I have published already. There are no transformers / ferrites in the signal path, so the amplifier should be immune to modulation from transformer or fan magnetic fields. Output power is > 13 dBm. The 7th channel is for cascading or for feeding that 1pps generator. There is also a new low noise preamplifier for phase noise measurements and inspecting noise behaviour of voltage references and such. http://www.bilder-hochladen.net/files/9hqp-6-jpg.html Stages are 3 pairs of SSM2210, cascode, AD797, AD797 and an Opa2132 for *1 Gain and offset regulation. Gain is *1 for phase detector calibration & 60 & 80 dB. Can be made smaller if wanted. The *1 output is always available and DC coupled if needed for VCXO locking. Bandwidth is >1 MHz completely flat with any gain setting. lower BW corner is abt 0.5Hz or DC if the offset loop is defeated(but switching this off makes only sense for lower gains). Noise is the expected 700 pV/sqrtHz. The high gain path can absorb upto 20 mV offset as it is currently dimensioned. All interesting I/O points are on a 100 mil grid, so the amplifier can be used as a "macro" on predrilled board (like Vero Powerplane (r)) if the shielding is to be done for the whole assembly. All switching is performed with gettered bistable relays. Monostable relays had too much power dissipation, messing up the offset when switched on or off. It's fun when your scope setting reads 200 nV / div and you still have a meaningful display, at least for small bandwidth. regards, Gerhard