# Voltage Controlled Oscillator: Maxim vs Crystek

1. Sep 19, 2010

### jd254

I need to build a circuit and it requires Maxim's MAX2623 VCO. I need to mod my circuit so the frequency the VCO would run from 850 to 2100 MHz. Maxim doesn't supply or make such, but Crystek does. I found Crystek CVCO55BES-0950-2050, which runs at 950 to 2050 MHz. This is good enough since 1900MHz is the most important frequency I need it to run at.

I just have one problem. Maxim's data sheet shows the MAX2623 comes with 8 pins, while the CVCO55BES only comes with 3... technically 16...

My schematic uses 5 pins from the MAX2623: Tune (pin 2), SHDN (pin 4), VCC (pin 5 and 6), and out (pin 7).

On the CVCO55BES, it has only 3... RF, Vcc, and Vt.

1. Am I safe to assume RF is the output, and Vt to be Tune?

2. What's SHDN? (Shutdown. Low-power standby mode?)

3. How do I handle the Vcc? I have two wires on my schematic, one going to pin 5 and one going to pin 6. I only have one opening for Vcc on the CVCO55BES.

here are the data sheet for MAX2623 and CVCO55BES respectively:

http://datasheets.maxim-ic.com/en/ds/MAX2622-MAX2624.pdf"

thank you for helping

Last edited by a moderator: May 4, 2017
2. Sep 19, 2010

### vk6kro

I just have one problem. Maxim's data sheet shows the MAX2623 comes with 8 pins, while the CVCO55BES only comes with 3... technically 16...

My schematic uses 5 pins from the MAX2623: Tune (pin 2), SHDN (pin 4), VCC (pin 5 and 6), and out (pin 7).

On the CVCO55BES, it has only 3... RF, Vcc, and Vt.

The other pins have to be grounded, so it is really 16 pins. They also recommend a ground plane under the chip. The "pins" are only flat pads on the bottom of the chip and they will need some delicate soldering and they will be very difficult to unsolder.

1. Am I safe to assume RF is the output, and Vt to be Tune?

Yes

2. What's SHDN? (Shutdown. Low-power standby mode?)

Shutdown. It is mentioned at the top of the document.

3. How do I handle the Vcc? I have two wires on my schematic, one going to pin 5 and one going to pin 6. I only have one opening for Vcc on the CVCO55BES.

Just use one of them. The Maxim unit gave the option of running different parts of the chip on different supplies, or on the same one if you bridge the Vcc inputs together.

This looks like an amazing chip, but it will be very sensitive to voltage variations on the tuning line. At 80 MHz shift per volt, even a few mV of noise or junk voltage on this line will produce lots of FM.

3. Sep 19, 2010

### jd254

Thanks for the advice. I guess I'll be buying the adapter that comes with it... gotta look for it...

so... I should just bridge the two wires going to pin 5 and 6 together and attach it to the Vcc?

Hm.... I wanted a wide range so I have options... but I feel you're trying to tell me I might face a problem holding a precise voltage, which will probably render my device useless if so... ok, I'll find a small range near 1900MHz instead. Now if Maxim only created a 1900MHz VCO, I'll be set.

4. Sep 19, 2010

### vk6kro

The Vcc is just 5 volts and your other chip has two 5 volt leads going to it.
So, you just need one of them for the new chip. No need to bridge them together, but you will need a bypass capacitor right at the chip's Vcc input.
If you could get the chip already mounted on a PC board designed for it, that would be better than trying to make it from the parts. These frequencies are full of bad surprises.

Yes, the device will be great for wideband coverage, but it would be super-sensitive to noise on the tuning line.
So, say it was used for a spectrum analyser, you might find it difficult to zoom in on some signal once you found it.

Do you know the price for this chip?

5. Sep 21, 2010

### jd254

1. when u say bypass... do u mean the capacitor should be attached in parallel or in series before the Vcc input?

2. I found this:

http://www.crystek.com/microwave/spec-sheets/vcoeval/CEVAL-033_055.pdf" [Broken]

It doesn't seem to be plug and play... do I still need to solder? EDIT: I just read the data sheet... soldering required lol oh well. I'm sure I can handle it under the watchful eye of one of my professors.

I also found this:

http://cgi.ebay.com/Designer-Kit-fo...tu=UCC&otn=5&ps=63&clkid=5526283176685129194"

3. The VCO is priced around $30 but can be found for cheaper. The VCO board is$40 roughly... can't find a cheaper board.

Last edited by a moderator: May 4, 2017
6. Sep 21, 2010

### vk6kro

It looks like the underside of the chip has to be soldered to that flat surface on the PC board.

This is specialized stuff and maybe you could get it supplied already mounted and tested, even at extra cost.

See capacitor C2 on the board diagram. That is a bypass capacitor.

7. Jul 29, 2011

### ViralDoshi89

Hello Can anyone help me with one doubt that is arising during the process of making the

voltage control oscillator I have brought the crystek CVCO55BES-0950-2050 IC and I need the

circuit schematic to run this IC from which I can tune any frequency between 950 - 2050 MHz.

Well can jd254 help me with this because you sound successive so far can you land me your schematic which works with CVCO55BES-0950-2050. I will be very thank full to you...