looking for a suitable vco

[[email protected]]

Hi,

In my project, I drive an oscillating device (oscillator) with an VCO
reference signal. In order to lock the oscillator's frequency, a PLL is
employed. To keep the device oscillating the input frequency needs to
be hit at least as precise as 0.005 Hz.

The problem, though, when the oscillator is changed, its center
frequency changes, too. It can be in the range between 11.75kHz-12kHz.

Because of other clocks that need to be synchronized and generated, the
VCO's output frequency must be in the range 13.865-14.16 MHz. Actually,
a VCXO would fit my needs best to tune the frequency as accurate as 5.9
Hz at 14 MHz (0.005 Hz at 12kHz). However, if I pick a VCXO for say
14.1 MHz that is +/-100ppm pullable, it may work with some oscillators,
but not with all possible.

So, I need a VCO whose center freqency is coarse adjustable in a
relatively wide band (13.8-14.2 MHz) and it should have a fine
frequency tuning resolution using the input voltage.

Has anyone an idea what VCO could fit for this?

Thanks,

Stefan

 

[[email protected]]

Hi,

In my project, I drive an oscillating device (oscillator) with an VCO
reference signal. In order to lock the oscillator's frequency, a PLL is
employed. To keep the device oscillating the input frequency needs to
be hit at least as precise as 0.005 Hz.

The problem, though, when the oscillator is changed, its center
frequency changes, too. It can be in the range between 11.75kHz-12kHz.

Because of other clocks that need to be synchronized and generated, the
VCO's output frequency must be in the range 13.865-14.16 MHz. Actually,
a VCXO would fit my needs best to tune the frequency as accurate as 5.9
Hz at 14 MHz (0.005 Hz at 12kHz). However, if I pick a VCXO for say
14.1 MHz that is +/-100ppm pullable, it may work with some oscillators,
but not with all possible.

So, I need a VCO whose center freqency is coarse adjustable in a
relatively wide band (13.8-14.2 MHz) and it should have a fine
frequency tuning resolution using the input voltage.

Has anyone an idea what VCO could fit for this?

Have a look at a digital phase locked loop controlling an Analog
Devices direct digital synthesis chip. The original was the AD9850

http://www.analog.com/UploadedFiles/Data_Sheets/AD9850.pdf

but the range is now huge. The cheapest, slowest part - the AD9833 - is
probably too slow, with a clock frequency of 25MHz, to produce a
respectable looking 14MHz clock. Something with a clock frequency
closer to 100MHz would make life a lot easier, but you'd still have to
be pretty careful with the design of the anti-aliasing filter. Happily,
the Aanlog Devices range goes up to 1GHz, albeit at a similarly
astronomical price.

 

[[email protected]]

Hi,

a dds seems to be a good choice. But i need to program the dds's output
frequency with an microcontroller which means, that I need to transfer
parts of the PLL into software, right?

Thanks,

-Stefan

 

[maxfoo]

Hi,

a dds seems to be a good choice. But i need to program the dds's output
frequency with an microcontroller which means, that I need to transfer
parts of the PLL into software, right?

Thanks,

-Stefan

You could use the DDS as a reference frequency for a PLL/VCO, or just use a DDS
alone. try the analog devices 98xx series they have very good phase noise specs.