Hi guys,

I am looking for a one GHz plus IC oscillator. I preferably would like a square wave to be outputted. I have previously used the 555 IC oscillator, however that is only in the MHz range and not appropriate for my application (laser distance measurements using time of flight principles). If someone knows of a one GHz IC oscillator that is simple to use like the 555 IC oscillator (i.e requires only a handful of peripherals in resistors and capacitors) can they please indicate. Thanks in advance for any replies,

Regards,

Ping!

 

You may already be aware of this but designing circuits in the GHz range is a whole different ball game. Capacitive reactance becomes low and things like the dielectric strength of the circuit board material becomes important.

Good luck with it though

 

I doubt that one exists. It is not unusual to start with a lower reference frequency and use that with a VCO and a PLL to achieve the higher frequency. It is also possible to use multiple stages of frequency doubling or tripling. This will be a challenge whatever you do.

 

Hello,

there are some vco's of mini-circuits that could make 1000 Mhz:
http://www.box73.de/product_info.php?products_id=730
http://www.box73.de/product_info.php?products_id=1212

Bertus

 

Here is Mini-Circuits USA site:
http://www.minicircuits.com/homepage/homepage.html
They have quite a selection of VCO's from 3MHz to 7GHz at what seem like bargain basement prices.

 

I stand corrected, but it is still the case that not every basement experimenter can grab one of these parts and get something working.

For Example, this non-surface mount part might be suitable.

http://www.minicircuits.com/pdfs/POS-1400A.pdf

A couple of questions for the OP, to see if you understand the data sheet and can adapt the part to your needs.
1. What power supply(s) would you propose to use?
2. What control voltage will give you a 1.00 GHz. output?
3. How much power will the oscillator produce at 1 GHz.?
4. How do you plan to couple/terminate the output?
5. What voltages and currents will appear at the output?
6. How will you amplify them?

 

Thanks guys for the support. I will chase up the VCO's. "Papabravo" I have not got that far yet, if I manage to get something to work I will post all the details.

 

To answer some of my own questions
1. I would use a 24V main supply with regulators to supply a 8V Vcc and for experimentation, an adjustable 1V to 20V output. The current requirement for the adjustable 1 to 20V should be much less than the 8V Vcc (30 mA).
2. Linear interpolation suggests that ≈ 5.7 volts should produce 1 GHz at room temperature (25° C)
3. The power output is 12.92 dBm which according to HS algebra should be ≈ 19.6 mW
4. For experimentation, you terminate it with a surface mount 50 ohm resistor. A 1/10th watt should be fine.
5. Across the 50 ohm terminator you might see about 1V @ 19.8 mA
6. Check the minicircuits catalog for an amplifier with a 50 ohm input, a suitable amount of gain, and a 50 ohm output.

Not quite as easy as a 555 but doable.

 

Some food for thought Papabravo, tanks, will keep use posted as to how I go!

 

Many thanks Papabravo for your input !!!

I have since went on to buy a CRYSTEK VCO (CV055BE-1550-2050) and have wired it up. Not sure it is going to work so thought I would see what you or someone else who has a good understanding thinks. I have attached the specs of the CRYSTEK VCO (CV055BE-1550-2050) and a wiring diagram of my circuit. At this stage all I want to achieve is see a oscillating output signal using a spectrum analyser, just to make sure I have understood how to wire everything up.

The relevant specs of the CRYSTEK VCO (CV055BE-1550-2050) are as follows:

* output frequency range 1550-2050 MHz
* tuning voltage (Vt) range 0.5-15.5 VDC
* supply voltage (Vcc) range 7.6-8.4 VDC
* supply current range 17-30 mA
* output power typ. -2.5 dBm

As you can see in my circuit diagram I use 9 V batteries and voltage regulators for Vt and Vcc. The tuning voltage (Vcc) is set at 9 V which should lead to an output signal frequency of 1800 MHz or so. With a terminating resistance of 1.4 Ohms I should see a voltage across this resistor of 28.117 mV with a current of 20 mA. The calculations to obtain these numbers are as follows:

The output power of the CRYSTEK VCO (CV055BE-1550-2050) is typically -2.5 dBm. This translates to 0.56 mW (from 10^(-2.5/10)), I assume this is an average power? Setting the output current to 20 mA the terminating resistance can be calculated using R=P/I^2, where R is the terminating resistance, P is the output power and I is the output current, therefore R=1.4 Ohms (0.56*10^-3/((20*10^-3)^2)). From here the voltage drop across the terminating resistance is found to be 1.4*20*10^-3 which equals approximately 28.117 mV.

So if everything is correct I should see an output wave across the terminating resistor of approximately 1800 MHz with a voltage of 28.117 mV or so? Will this indeed be the case? Am I missing something in the circuit I have put together?

Thanks in advance for any replies.


View attachment OscillatorCrystek.pdf

 

Hello,

You made one mistake in connecting the VCO.
RF circuits are normaly terminated with 50 Ohms.
You have connected a 1.4 Ohms resistor on the output wich is way to low.

Also what regulator are you using for the 8 Volts?

Bertus

 

Thanks Bertus, yes will go with the 50 Ohm terminating resistor.

The voltage regulators I am using are as attached in the specification (TO-220 variants),

Thanks.



View attachment CD00000444.pdf

 

Hello,

Looking at the datasheet, the 8 Volts regulator needs at least 11 Volts for input and the 9 Volts regulator needs 12 Volts as input,
With a lower input voltage, the output voltages will be also to low.

Bertus

 

I doubt that one exists. It is not unusual to start with a lower reference frequency and use that with a VCO and a PLL to achieve the higher frequency. It is also possible to use multiple stages of frequency doubling or tripling. This will be a challenge whatever you do.

Even PLLs get a bit like plumbing at GHz frequencies, an old favourite is the multistage frequency multiplier, a tuned amplifier with the input tuned to the standard frequency and the output tuned to one of the higher harmonics.

Another multiplier is based on varactors - I don't know much about those, but they're a favourite with some amateur radio operators. Hopefully that's a hint where to look for more info.

 

Thanks Bertus, of course the voltage regulators need an input voltage that is over a certain thresh-hold so they can work properly.

OK think I got this VCO up and running. I will proceed with using a counter now to count pulses, hopefully simple and do not need to do too much by way of filtering, i.e differential?

 

Hello guys, once again thanks for all the support.

Ummmmmm, just not sure on one thing, might not be an issue. The Crystek VCO (specification attached) which I am using states that the supply current should be typically 17 mA and not exceed 30 mA. Does my current circuit (diagram attached) ensure that the maximum supply current is not exceeded? The voltage regulator feeding the supply voltage (Vcc) to the VCO has specifications of:

* output current = 5 mA to 1 A, input voltage = 10.5 to 21 V (for the L7808C, specification attached)

Do I need to add in a resistor to ensure the 30 mA maximum supply current to the VCO is not exceeded?

Thanks in advance for any replies,

Regards,

Ping.


View attachment OscillatorCrystek.pdfView attachment L7808C.pdf

 

I got an answer from Crystek regarding my recent question, they said no resistor is required.