4046 PLL question

I think this is addressed in Appendix B of TI's app note on the 4046, SCHA003B is the document name.

They say that before lock, when the correction is only in one direction to slew the frequency, that the Vcc/(2pi) is the gain. But after lock, when the corrections are small pulses and not always in the same direction, and the correction is made from roughly (Vcc/2), then Vcc/(4pi) is more appropriate.

Tim.

A short question on the "Type 2" phase detector: On page 648 of AoE it says that this detector has a gain of VDD/(2*pi) which I find plausible because the lowpass output goes from 0V to VDD as the phase difference of the input signal goes from -pi to +pi.

However, both the ON semi and the Philips datasheets say that Kp=VDD/(4*pi). I double-checked and made sure that all three sources talk about the 4046's output pin # 13.

Why the discrepancy?

robert

AoE is obviously referring the 4046 PC3 phase comparator, and the datasheets are referring to the PC2 phase comparator. The PC3 is a toggle FF, and the PC2 is a dual FF phase/frequency comparator.

Your lack of comprehension. These datasheets are full of self-explanatory graphics, equations , and write-ups.

You don't say what family 4046 you are using. The HC/HCT parts are quite different, depending on manufacturer. Just look at the max frequency to get a clew. I think the Moto (ON), and the Philips were the most alike.

Tam

Tam

[snip]

Wrong number, make that MC4044.

...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 | |

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

On Mon, 01 Aug 2005 12:58:59 GMT, Fred Bloggs wrote in Msg.

No. They refer to the same pin number (13), and Fig. 9 in the Philips data sheet corresponds to Fig. 9.69 in AoE. They clearly both refer to what Philips calls PC2. Fig. 11 (Philips) shows the output of PC3, which is not what AoE talks about.

According to Philips, PC2's gain is Vcc/4pi, but AoE says it's Vcc/2pi.

I'm trying to rectify that.

robert

Sounds like something written by an apps engineer without a clue.

...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.

Keep in mind that pin 13 (whatever your particular data sheet calls that phase detector) is high impedance most of the time in lock, and only low impedance while the thing is detecting phase mismatch. The thing is designed to connect like this:

| | to VCO|--------------. | ___ | pin 13|------|___|---o | | | | | --- --- | | === GND created by Andy´s ASCII-Circuit v1.24.140803 Beta

(note that what I'm saying is still valid for more complex loop filters). The charge pulse that gets injected into the capacitor is dependent on the voltage across the capacitor as well as the phase error

-- so if the cap is sitting at 1/5 VCC then it will have a 4:1 difference in the response to a phase error in one direction as it will in the other. You need to take this into account when you design your loop filter, usually by including lots of extra gain margin.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Yup. I had found out by now, too. It's not really that difficult; I was just confused.

robert

The best embodiment is that the phase detector output is a current source/sink.

Or work the 4046 "switches" thru a resistor into a virtual ground.

...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.

The better PLL chips have some magic circuitry* to make them look like controlled-current sources when they're active, rather than hard shorts to ground or VCC. To get the same effect with a 4046 you'd have to work into an op-amp with a virtual ground, and you'd have to take the op-amp's noise into account in your circuit design.

• that's what you do, Jim -- you put the magic into the little black bugs; I just use them.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Andy asks Jim :

Were you working with Jon deLaune at the time ?

Andy

I can't remember when I didn't use current source/sink for PD outputs.

Yes I can, the original MC4044 used R's into a fed back Darlington.

...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.

I remember the name, but he was in another group... maybe applications?

I was in analog research/design at Motorola.

Do you know Jon from somewhere?

...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 | |

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

If there's anything missing from the modern line up of tiny-logic chips it's a 4046-style phase detector (or better yet one with controlled current outputs) it the World's Smallest Package. My dream chip would have six pins: VSS, VDD, in1, in2, phase out and current program (which could be tied high to emulate the 4046 phase detector). This would all come in a SOT-23 package or a flip-chip.

At the moment if you want just a phase detector you have to use a 4046 with a disabled oscillator and use up extra space not only for the chip but (possibly) for the aforementioned virtual-ground op amp integrator.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I remember seeing his name on the patent, and I think it was for the MC4044. I just went to the uspto.gov site, but they only go back to 1976, so I can't verify it just now..... I definitely saw his name on the Motorola app notes for the 4044 , way back in the early 70's . ( Funny, the stuff that sticks in your mind (grin) )

Whoever did it, the 4044 was a fine piece of work that was a major breakthrough in the development of frequency control... I was designing frequency synthesizers at the time for Bendix Avionics, then later for Texas Instruments. I used the 4044 in a dozen products, then I started building my own with two D's and a reset gate ( same 4044 circuit using D's instead of individual gates --- gave me better control over the dead zone)..... Later I expanded it into a quad of D's which gave slightly better pump action when the frequencies were widely separated ( Principles of Three State Phase Detection - EDN- Sharpe ).

But I have always credited the 4044 development with the same sort of genius as the light bulb, sliced bread, and peanut butter with chocolate......

Before the 4044, we were using slip counters for frequency/phase comparison ( Fairchild applications note dealing with avionics - John Nichols ) and they were a pain in the ass to analyze. The 4044, especially when used with an op amp, made the analysis very straightforward..... Later versions in CMOS (4046) had more pump voltage and lower leakage. I couldn't get a hold of the dead zone problem , and leakage, until I started building them out of separate high speed flipflops.........

Just reminiscing, and the mention of your involvement with the 4044 yanked my crank enough to respond....

Andy Sharpe

Andy responds to Tim:

I would prefer separate outputs for the phase detector Pump up and pump down, (which I could tie together if desired ). And a pin for a lock detector, rudimentary tho it would have to be......

I Andy Sharpe, retired, PE, etc........

Sorry, Jim, I just found the patent reference....... I remembered that I had referred to Laune's patent in the patent search I provided for my quad D patent.....so I looked up mine and got the following numbers from it..... :

Laune patent # 3714663 Jan 1973

I couldn't read the text cause my laptop doesn't have the plugin for it. Full text isn't on the gov pat server until 1976..

You might want to read it to see if you should've gotten credit for it (grin).... If this is truly yours, ....... thanks for making my life a lot easier.....

Andy Sharpe ( aka Claude Andrew Sharpe)

Hmm. But now you're up to 8 pins, and those packages take a jump in size.

Good point, though, and it sounds like you've done this a lot more than me.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com