discrete CRT character vector generator? Maybe Tek style?

[james_s]

Were these ROMs programmable in some fashion (mask?) or was the data baked into the layout of the IC? It's interesting that they went with this approach rather than a more conventional ROM feeding a resistor DAC.

[David Hess]

Were these ROMs programmable in some fashion (mask?) or was the data baked into the layout of the IC? It's interesting that they went with this approach rather than a more conventional ROM feeding a resistor DAC.

There is no DAC.  An earlier stage produces a sawtooth waveform which is fed into the analog ROMs, along with a digital address, and that produces a set of X and Y outputs which are functions of the sawtooth input.  Each character is then made with a series of curved strokes.

The analog ROMs are programmed using resistor values and emitter areas, so like a mask ROM.

[james_s]

Were these ROMs programmable in some fashion (mask?) or was the data baked into the layout of the IC? It's interesting that they went with this approach rather than a more conventional ROM feeding a resistor DAC.

There is no DAC.  An earlier stage produces a sawtooth waveform which is fed into the analog ROMs, along with a digital address, and that produces a set of X and Y outputs which are functions of the sawtooth input.  Each character is then made with a series of curved strokes.

The analog ROMs are programmed using resistor values and emitter areas, so like a mask ROM.

Yeah I get that there was no DAC, I meant I'm surprised they didn't just use a DAC, although maybe conventional ROMs were still too primitive.

[David Hess]

Yeah I get that there was no DAC, I meant I'm surprised they didn't just use a DAC, although maybe conventional ROMs were still too primitive.

They used their own ADCs which implemented 1-of-10 encoding, so like a flash converter but with only 10 levels or 3.3 bits.  One of the later compatible implementations uses 3-bit DACs to define the endpoint of strokes within the character cell.

[Martinn]

Update:
I found out that by far the best information on Gilbert's analog ROMs is the patent: https://w140.com/tekwiki/wiki/Patent_US_3651510A
It really is well written and entertaining to read! Unfortunately, duplicating the functionality with discrete components is pretty difficult, but I'll try anyway.
For experiment 1 I replaced the multi emitter triples with three transistors with adjustable degeneration. The remaining control like the vector blending is mostly identical to the ROM version.
On the scope XY plot you see it drawing a "M" character, which needs only five of the eight available points. In the signal plot to the right you can see that the blending does not give the nice linear shapes as Gilberts analog ROM, which IMO is caused by the degeneration resistors. Also there's some noise on the signal - I'll have to find out where this comes from. But overall this works.
Of course this is just one character! For multiple ones, one would have to use fixed resistors and a more compact layout. I wonder if the total capacity of such an array would be prohibitive.

Many of you have commented why I bother with this old stuff and not just solve it digitally. The reason is that I do that all day long and it would be straightforward for me. On the other hand, I know noone in my line of work who could still do analog BJT designs (not just switching on a LED). This kind of knowledge at least where I work got mostly extinct.

[David Hess]

That is great that you got usable results.

In the signal plot to the right you can see that the blending does not give the nice linear shapes as Gilberts analog ROM, which IMO is caused by the degeneration resistors.

Using emitter degeneration does not give quite the same effect, and Gilbert had the advantage of integrated transistors which have matched Vbe and hfe.  You should get significantly better results if the Vbe of each transistor in a set is matched, along with the use of a reference transistor for each set.

[Tomorokoshi]

Is the oscillation noise because there is no bypassing on the board? How long are the leads from the power supply?

[HarryDoPECC]

Late to the party (as usual!)

I work with vintage calculators, at the start of the 1960's Friden produced the EC-130 - in my opinion the most attractive machine of that era.  See it on my site:  https://dopecc.net/calculators/friden/ec130/  On the photos tab you will find a picture of its multi-line '7-segment' style display,  generated on a CRT.

The entire display circuit is analogue and discrete, just as the OP is seeking.  Elegant and subtle work.  Designed by Stanford Research Institute for Friden.  Can't find the patent just now.  I have a number of these machines and the displays still work well in machines with 50yo components. 

I have attached an original Friden's Service Note where the principles are described in a uniquely chatty way.

If OP wants a real challenge, consider if this could be extended to 12-segments, which would give a fair alphanumeric substrate.  Note that part of the extended scan is already present....
Otherwise, just enjoy the engineering of that era.

[Martinn]

Bypassing: Yes, I noticed that when I had ordered the boards. Just added two decoupling capacitors - much better!

Friden calculator: Nice idea. Beam deflection is fixed to the segment pattern, blanking is generated via a diode ROM. Interesting!

[Martinn]

And a letter "2". Quite a flowery script...

[Martinn]

And here's experiment 2.
You cannot replicate multi emitter resistors with discrete components, but you can connect them in parallel, which should linearly scale their transconductance.
The patent states that for all combinations, 8-10 emitters should be connected in total. So here I have eight transistors per point. The slide switches connect the collector to one of the X, Y and Z lines. If you want to have a square character matrix, this gives you a range of 0-4xIC for the X and Y lines, so a grid of 5x5 total. This is somewhat limited compared to the Gilbert ROM, but should be sufficient nonetheless.
And here is another "2" try:
Much better than the potentiometer version.

BTW now you really should see why I love PCBA services (JLCPCB)... no more hand soldering for me!