Chris Christopher Hoover wrote: >> The TI regulators are, from my perspective extremely noisy, one can do >> much better at least for higher output voltages. >> They also don't have a high enough output for the TADD-1. >> > > Agreed, that that regulator doesn't have sufficient margin for the entire > TADD-1. > > I was suggesting using the low-noise high PSRR linear reg only to establish > the bias level. > > There are indeed better parts. This one looks pretty good for an > integration solution (not include three C's): > > http://datasheets.maxim-ic.com/en/ds/MAX6126.pdf > > This app note, which filters the MAX6126 with an additional pass transistor > and opamp, shows how to get down to 6 nv/sqrt(hz): > > http://www.maxim-ic.com/appnotes.cfm/appnote_number/3657 > > That circuit is only for about 3.2V output, you can do better for higher output voltages using the same technique with a buried zener reference. The TADD-1 has a 9V supply and requires a 4.5V reference. A 10V supply with a low dropout low noise regulator would be better as one could then obtain an output of slightly more than 1V rms instead of slightly less. >> < other circuit suggestions > >> This avoids blowing fuses if the supply polarity is reversed. >> > > Or a PZT. We use a lot of them in the power circuit for hot plug sockets, > like on disk shelves. (A fuse is cheaper wrt to the BOM, but the warranty > costs kill you.) > > >> The problems of instability and coupling of power supply noise into the >> signal path were also present when single supply discrete transistor >> amplifier were the norm. >> Quite elaborate bias divider decoupling circuitry was used to minimise >> the effect. >> > > Yeah, at some point a bipolar design becomes easier, right? > > -ch >
Yes, an isolation amplifier consisting of a cascade of 3 stacked common base stages with transformer coupled inputs and outputs should achieve an input output isolation of 120dB or so at 5-10 MHz with a total power supply requirement of around 20mA @ 24V per amplifier independent of the load (open circuit, 50 ohms or short circuit). 6 such amplifiers would required about 120mA @ 24V, considerably less power than a fully loaded TAD-1. Having the power supply current independent of the output loading is also advantageous. The phase noise floor should be -174dBc/Hz or lower with 13dBm input and output. The amplifier delay tempco should also be very low (~1-3 ps/K). This configuration could be redesigned for 12V operation but would required transformer coupling the output of the input common base cascade pair to a pushpull common base output stage. Power requirements would then be about 60mA @12V per amplifier or 360mA @12V for 6 amplifiers independent of the the individual amplifier load impedances. Performance would be degraded slightly with a phase noise floor a few dB (1-2) above that of the equivalent 24V amplifier. Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts