J
Jure Newsgroups
- Jan 1, 1970
- 0
Winfield said:It's got 16 parts - too many for an ASCII schematic.
I'll see about putting it up on our public ftp site.
BTW, the parts are all inexpensive.
Basically it's the bf862 with a ferrite in the gate,
a source resistor to Vee for running at 5mA, a drain
resistor plus bypass cap to gnd to reduce the drain
voltage to under 8V (see datasheet), a coupling cap
to an emitter-follower stage, which is biased at say
-10V, depending on the PD, an LC filter to quiet the
bias-voltage source, a pos/neg bias-voltage header, a
low-noise EF BJT, with resistor to run at 4mA, etc.,
with back-back collector pmbfJ309 JFETs to limit the
current in the event of a PD-sensor short. Finally
there's another ferrite at the output to damp parasitic
RF oscillations (small resistors, commonly used for this
purpose, aren't allowed because of their Johnson noise).
The bootstrap follower has an 80MHz bandwidth, probably
limited by the ferrites, and is capable of driving the
guard shield in a triple-coax cable, etc. Armed with
a pencil, one should be able to draw the schematic.
WH >> a coupling cap to an emitter-follower stage,
Do I read correctly, AC coupled ?
Jure Z.