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Simple crystal (4.43MHz - PAL) oscillator + PLL multiplier circuit wanted.

Per the subject line. I want to experiment with direct PAL video generation from a microcontroller, with the minimal number of parts. I'm thinking that a good starting place might be to use a CPU clock that's based on the PAL subcarrier frequency (4.43MHz) multiplied with a PLL+VCO+Divider to give me phase reference points, & directly generate the composite colour signal via an R2R ladder.

So, some questions:

1) Is this a reasonable concept? (I'm comfortable with per-cycle level timing & coding)

2) Any tips/suggestions/thoughts as to a better approach?

3) What's a good (simple, cheap, stable) circuit to oscillate a standard 4.43MHz PAL sub-carrier xtal? (Ideally just an inverter or two)

4) Suggestions for a cheap + simple PLL frequency multiplier (x8? x4?) for the above to give me multiple cycles per PAL subcarrier cycle?

5) How many analog samples do you actually /need/ to generate per subcarrier cycle to get good quality PAL colour?

6) Any recommended online resources/references that cover direct digital synthesis of medium to high quality PAL colour video?

Thanks in advance for any help or advice.

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   W  "Some people are alive only because it is illegal to kill them."
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Reply to
Lionel
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Normally PAL/NTSC is samples at 4 times subcarrier. There are some genlock ics around see here:

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You may have to find out all the joys of the "eight field sequence", fortunately, I have forgotten most of it, it's messy.

Maybe you should think about working in YUV/component/RGB, which has no subcarrier, but is sampled at 27M/sec, and is easier than PAL

List of chips:

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martin

Reply to
martin griffith

A few people have had (limited) success with direct composite PAL video generation directly from a micro, like this one:

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Ordinary quality, but shows that the minimum parts count is a PIC and two resistors! Much faster micros are available would obviously do a bit better than the PIC.

Dave :)

Reply to
David L. Jones

one:

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Note that his _PIC_ solution is BW only, he does color on a SX micro: with an about 53MHz clock(12x Fc )

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There are several cheap PAL modulator chips, so a PIC and for example a MC1377 modulator chip would be 'low chip component count'. MC1377 is old, and uses a 4.43MHz xtal, quality is good enough for games.

The alternative is a PIC and a sparate 8.86 MHz (2xfc) oscillator, some 4053 switches, some 4013 FF, some inverters and xor gates to make a PAL modulator. I'd use the MC1377:-) Or you need a very fast PIC !

Reply to
panteltje

In the dark recesses of my past, I remember owning a ZX80....

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--
 - René
Reply to
René

You might want to consider the converese of that. 20+ years ago it was common in cheap computers here to start with an oscillator at 14.318 MHz, which was then counted down to the NTSC color subcarrier frequency of 3.579 MHz. 14.318 is also an integral multiple of the horizontal and vertical sync frequencies. I see that 17.734475 is a standard crystal frequency. Is that

4x the actual PAL frequency?

Tam

Reply to
Tam/WB2TT

On a sunny day (Mon, 05 Mar 2007 14:19:25 +0100) it happened René wrote in :

I had one too, and it was BW. It had a Z80, at 3,58 Mhz or so, and a custom ship with the shift register in it. One of the best BASICS ever, the Z80 refresh register was also used for the display. It was followed by the ZX81 (Timex1000 in the US), and I still have the book Timex1000 / ZX81 ROM dissasembly by Dr Ian Logan and Dr Ohara. Even controlled an audio switcher with it.... ZX81 was BW too. Later came the Spectrum, never had one, but _that_ one was color I think.

Reply to
Jan Panteltje

"Tam/WB2TT" wrote in news:rZmdnRzdcY3yuHHYnZ2dnUVZ snipped-for-privacy@comcast.com:

I believe it is. 4.43361875Mhz

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

Yes, it is. However, I don't know if it's high enough to give me enough samples to create a clean Chroma, etc. I'm pretty sure that I'll need to sample at a minimum of 8x (35.468950MHz) the base colour subcarrier frequency. I /hope/ I won't have to go as high as 16x (70.937900MHz). ;) That said, using 17.734475MHz means I'd only have to multipy it by 2 or 4 to get my higher multiples, which may make life easier.

--
   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
  \|/  \|/              Perna condita delenda est
---^----^---------------------------------------------------------------
Reply to
Lionel

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may be of interest

martin

Reply to
martin griffith

Unfortunately, it's not accessible:

------------ Forbidden You don't have permission to access /pip/SAA7121H_V2.html on this server. Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.

------------

Fortunately, Philips have it on their shiny new marketeer-flavoured website:

--------- General description The SAA7120H; SAA7121H encodes digital YUV video data to an NTSC or PAL CVBS or S-video signal. The circuit accepts CCIR compatible YUV data with 720 active pixels per line in 4 : 2 : 2 multiplexed formats, for example MPEG decoded data. It includes a sync/clock generator and on-chip DACs.

---------

Looks interesting. Thanks Martin.

--
   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
  \|/  \|/              Perna condita delenda est
---^----^---------------------------------------------------------------
Reply to
Lionel

I've generated PAL and NTSC CVBS in a Cyclone II (5K) FPGA, $12.90 in singles. I load the FPGA with a 0.68 micro. Total parts cost: ~ $16.00 in singles w/ 8-bit DAC, ~ $17.00 for 10-bit DAC. Parts total in the

1000+ would be about $8.00. USB is about 1.50 extra if you need computer control.

Do you need genlock? If not, a simple xtal osc at 4x or 8x with inverter will work fine. Are you familiar with the PAL color subcarrier phase shift wrt the field sequence?

Frank Raffaeli

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Reply to
Frank Raffaeli

***************** That would still simplify things because you could use a frequency doubler, or two in series, and not have to worry about phase noise and such of a PLL. A 2N2369A, or the like, biased class C will work nice as a doubler at these frequencies. You would need a limiter on the output.

Tam

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Reply to
Tam/WB2TT

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