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Need VCO for 14 MHz PLL

Need to generate in phase and quadrature digital signals, locked to laser detector output at ~ 3.6 MHz (quite stable). Need reasonably high precision 90deg shift and 50% duty fator +/- a percent or so. Thought of building 4X multiplying PLL, followed by 2 bit quadrature divider. So, looking for VCO that will run at 14.4 MHz.

Seem to find lots of chips for cell phone and other VHF/UHF/uWave apps, and old standbys from 556 and 4046 family, but nothing that would work at 14.4 MHz. Suppose I could make a Colpitts or Hartley circuit using varactor diode for variable capacitance, but, hoping there is a chip that will do this. Checked Maxim, National, Motorola, Linear Technologies, Burr Brown, with no joy. Any other suggestions?

Thanks W Letendre

Reply to
W Letendre
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You could just buy a cheap commercial RF VCO from MiniCircuits or Emhiser or somebody, and divide it down as necessary. The AD9901 is a nice, very fast phase detector.

The 4x pll + divider is good, but you will get phase ambiguity that you'll have to repair somehow.

John

Reply to
John Larkin

Naaah! It's trivial to make a quadrature divider that has no ambiguity ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Fortunately, do not need to lock output signals "in phase" to input reference; suffices for application that output in phase and quad signals have exact 90deg phase match to each other.

Will check out MinCircuits; should have thought of those guys. They make a ton of solder-in RF "gadgets" as I recall....

W Letendre

Reply to
W Letendre

Fear that DCO would be too expensive for application. Will check prices, though; they may have come down since last time I looked at them.

W Letendre

Reply to
W Letendre

If "quite stable" means "crystal stable", and you don't need a large range, and you have the time for things to settle down, then take a look at VXCO's -- they're available from many, if not most, of the crystal oscillator folks. And they're nearly crystal stable themselves.

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply to
Tim Wescott 

--
http://www.minicircuits.com/dg03-228.pdf

http://focus.ti.com/lit/ds/symlink/cd74hc4046a.pdf

http://www.standardics.philips.com/products/hc/pdf/74hc7046a.pdf
Reply to
John Fields

HC will actually stand off about +7V, but the manufacturers won't tell you that ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson

Ordinary 74HC... is optimized at +5V, will work reasonably well down to +2.5V, but becomes like molasses at +1.5V

The I/C stuff I'm working on right now has 5V, 3.3V, 2.5V and 1.8V devices on a single chip.

Not yet. I'm installing wire baskets on ball-bearing glides in the cabinets right now :-(

But it's giving me ideas for the drawers. These commercially-made baskets have a cross piece in the back to maintain alignment of the ball-bearing glides.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

The DDS chip itself is cheap but you still need a reference frequency source that adds to the overall cost.

The minicircuit vco is about $20, if that's still too expensive look into designing your own vco.

Synergy Microwave has a few good references on vco design, if you want to take that route...

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Reply to
maxfoo

These days the multiplicity of supply-voltages is getting to be a real pain for the designer. For example, modern 2.5 and 1.8V cPLDs have a rather substantial power draw, and generally their supply is not well-made using a linear regulator from +5V. One ends up with multiple supply sources, often with special sequencing rules, and perhaps with surprise interactions, like the difference frequency between two switching regulators. A design I'm finishing now, a five-channel DDS frequency generator, has seven supply voltages... And it's meant to be well-behaved to the 10ppm level. What a pain!

--
 Thanks,
    - Win
Reply to
Winfield Hill

I'm working a project at 2.2GHz right now.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Hello W Letendre,

Look at digitally controlled oscillators (DCO). Analog Devices has lots of these. You basically follow with a simple filter that cuts off above your desired range, send it the frequency you want and that's it. I know that this sounds like buying a pre-cooked pizza (which we'd never do...) but if you want it done fast that may be the way to go.

Regards, Joerg

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Reply to
Joerg

I'm also working on a hearing aid (analog) with MEMS microphone on-chip.

But I've done a lot of work just above audio... RFID tags and lightning location equipment.

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson

Hello W Letendre,

That is the downside of DDS chips. They are expensive and that is why I dealt with them only once so far. You need one where the master clock is about 3 times your frequency or higher. Maybe you could scrape by with the AD9835 but that is still over $5:

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However, if you want 14MHz quad you'd need one with 200MHz clock or so, to be able to divide down. Those will be more in the $10 range.

If it's very cost sensitive you'll have to do your own PLL.

Regards, Joerg

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Reply to
Joerg

Hello W Letendre,

I don't want to spoil the broth here but since you mentioned cost: These are often well above the cost of a DDS chip.

Regards, Joerg

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Reply to
Joerg

X-Fab

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson

How about this: +5, +3.5, +2.5, and +1.25... just for the digital stuff. Then 16 isolated channels, each with +-18, +5, and +-2.5. Arguably 84 power supplies on one board!

John

Reply to
John Larkin

Hello John,

15MHz out of a 4046 is indeed pushing it. For the 4013 I'd use some faster HC stuff for better 0-90 tolerance.

Regards, Joerg

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Reply to
Joerg

Hello Max,

Yes, but that boils down to a crystal and a fast unbuffered inverter. Plus you can still rent out the remaining inverters from the six-pack. Ok, if you need a really quiet clock source you'd have to throw in a BFS17 but that won't set you back more than a dime.

It's not me who needs this VCO. But if it was me and it had to be low cost as the OP said I would certainly roll my own.

Thanks. Ulrich Rhode really knows his stuff. Got his Communication Receivers book.

Regards, Joerg

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Reply to
Joerg

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