PLL locking problem

[cici]

My PLL can not lock. I am using an Xor gate as the PD. And the VCO is
cross coupled VCO. Now the control voltage is in the tuning voltage
range of VCO, but it is an oscillation the same frequency as the
output of the PD. It should be a DC voltage when the PLL is locked.
What can be the problem? Thanks!

 

[Jim Thompson]

On 1 Dec 2003 08:45:29 -0800, wangllu@yahoo.com (cici) wrote:

My PLL can not lock. I am using an Xor gate as the PD. And the VCO is
cross coupled VCO. Now the control voltage is in the tuning voltage
range of VCO, but it is an oscillation the same frequency as the
output of the PD. It should be a DC voltage when the PLL is locked.
What can be the problem? Thanks!

And your loop filter is what?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

 

[maxfoo]

On 1 Dec 2003 08:45:29 -0800, wangllu@yahoo.com (cici) wrote:

My PLL can not lock. I am using an Xor gate as the PD. And the VCO is
cross coupled VCO. Now the control voltage is in the tuning voltage
range of VCO, but it is an oscillation the same frequency as the
output of the PD. It should be a DC voltage when the PLL is locked.
What can be the problem? Thanks!

disconnect the Vtune line and connect a power supply to the vco. then monitor
the loop filter output on a scope and see if the voltage switches at the tune
freq...




Remove "HeadFromButt", before replying by email.

 

[Simon]

Sounds like you missed out the low pass filter between PD and VCO.


On 1 Dec 2003 08:45:29 -0800, wangllu@yahoo.com (cici) wrote:

My PLL can not lock. I am using an Xor gate as the PD. And the VCO is
cross coupled VCO. Now the control voltage is in the tuning voltage
range of VCO, but it is an oscillation the same frequency as the
output of the PD. It should be a DC voltage when the PLL is locked.
What can be the problem? Thanks!

 

[cici]

I am using a RC low pass filter, which is followed by a source follower.

Jim Thompson <invalid@invalid.invalid> wrote in message news:<g9smsvcint1iak80v014l6lt2e6dug2fnj@4ax.com>...

On 1 Dec 2003 08:45:29 -0800, wangllu@yahoo.com (cici) wrote:

My PLL can not lock. I am using an Xor gate as the PD. And the VCO is
cross coupled VCO. Now the control voltage is in the tuning voltage
range of VCO, but it is an oscillation the same frequency as the
output of the PD. It should be a DC voltage when the PLL is locked.
What can be the problem? Thanks!

And your loop filter is what?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

 

[Jim Thompson]

On 2 Dec 2003 06:19:05 -0800, wangllu@yahoo.com (cici) wrote:

I am using a RC low pass filter, which is followed by a source follower.

Jim Thompson <invalid@invalid.invalid> wrote in message news:<g9smsvcint1iak80v014l6lt2e6dug2fnj@4ax.com>...
[snip]
And your loop filter is what?

...Jim Thompson
[snip]

And where is your *zero*?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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