EMRFD Message Archive 14675

Message Date From Subject
14675 2018-04-30 17:57:01 Rod how to drive SBL-1 from CMOS

Hi Allison,

What do your recommend for driving a SBL-1 from CMOS??

Any ideas would be appreciated.



14693 2018-05-01 09:25:34 Dana Myers Re: how to drive SBL-1 from CMOS
14695 2018-05-01 09:49:23 Graham / KE9H Re: how to drive SBL-1 from CMOS
You would be better off putting a ~180 Ohm resistor in series with each of
the three gate outputs, rather than a single 68 with the outputs in direct
This will force the current to divide equally across the three drivers.
The way you did the circuit, the one with the lowest Rdson could 'hog' the
current and maybe go over current. You have no way of knowing.
--- Graham / KE9H


14702 2018-05-01 13:01:34 Dana Myers Re: how to drive SBL-1 from CMOS
14713 2018-05-02 21:49:34 Jim Strohm Re: how to drive SBL-1 from CMOS
Yeahyeah, what Graham said!  Resistors on the output of each gate is a better idea, though it increases parts count.

Is the '08 used simply to raise the output level, or to wave-shape as well?  What does the summed output look like compared to the input, which I presume with CMOS at this frequency is pretty much a square wave with a little trash on the rising side in the VHF and UHF spectrum, which will mostly go away in the rest of the total circuit?

Would low-value pF snubber capacitors help?  Obviously we will not see perfect sine waves from CMOS and TTL-like devices, but that's not necessarily what we need to get the best performance from an SBL-1 type mixer.

We only care about what comes out of the pipeline when everything's said and done.

And in this particular case -- CMOS and TTL are relatively "don't care" devices as far as input and output impedances are concerned.  Would an MMIC on micro-stripline work better, or would it be cheaper at the end of the pipeline to use '08?  Obviously if this is built  "dead bug" something like a 2N3866 would be a much better choice than any MMIC.  And an '08 array like the original circuit would be better, too.


14744 2018-05-03 13:07:17 Dana Myers Re: how to drive SBL-1 from CMOS
14745 2018-05-03 13:27:47 Dana Myers Re: how to drive SBL-1 from CMOS
14746 2018-05-03 15:18:08 Bill Carver Re: how to drive SBL-1 from CMOS
I use 74AC540, octal buffers, to drive 23 dBm diode mixers: a fast rise/fall square wave produces mind blowing intercept and low conversion loss.

14747 2018-05-03 15:35:05 Dana Myers Re: how to drive SBL-1 from CMOS
14750 2018-05-03 18:56:27 Bill Carver Re: how to drive SBL-1 from CMOS
I used the diode mixers in my variation of G3XJPs STAR transceiver. First mixer is H-mode, the diode mixers were for the second conversion between the 5.2 Mhz first i.f. and the 15 KHz DSP second i.f. I had a handful of +23 mixers, so to eliminate some signal switching signals between transmit and receive I used two mixers, one for TX and the other for RX (unlike H-mode, the diode mixer i.f. port is DC coupled so works great as the 15 KHz second i.f.).

I used the whole AC540, half (four stages) driving each mixer. Vcc was bumped to 6 volts DC with its own LM317. Each of the four AC540 stages has a 47 ohm resistor to one MCL 1:2 turns ratio transformer. This develops almost 6V p-p with a 50 ohm resistive load on the secondary. After verifying that voltage into a 50 ohm load I pulled that load and connected the mixer LO port. The mixer diodes clip and the p-p voltage changes from the resistor, but you've satisfied the "available power" they ask for.

LO drive is a square wave whose power is a hair below the data sheet 200mW sine wave. But its rise/fall times is MUCH faster than the dV/dt of a since wave so the intercept is improved.

Bill - W7AAZ