Mini VCO

Mini VCO Test Board

Designing a mini PCB that powers a commercial VCO module and allows manual tuning of its output frequency via a variable voltage. Using test equipment to verify frequency response and documenting results.

Choosing a VCO module

Low to mid RF range (easy to measure: 500 MHz- 1.5 GHz) - practical, relevant, and affordable
5V or 12V bias voltage - industry standard for RF and analog electronics and easily generated, simple and not complicated
Tuning voltage of 0-5V - safe, easy to generate, less noise, and easy to plot
SMA output - industry standard and widely used.
In stock

Research materials

VCO concepts: An oscillator circuit can be modeled as shown in Figure 1 as the combination of an amplifier with gain and a frequency dependent

application: #60: Basics of Phase Locked Loop Circuits and Frequency Synthesis

ROS-1310C+

Within the frequency range for modern RF systems but not too high in order to minimize complexity: 1260 - 1310 MHz with ultra low noise
Tuning voltage range: 0.5-4.5V - in range with requirements
Supply voltage of +5V
Tuning sensitivity of about 100 MHz/V

(for every Volt increase, fout increases

by appx. 100MHz)

SMT 4 lead: simple and small

How to Power it

5V power in
Current draw: approx. 25mA(only for VCO)
Regulate without an LDO because its we would need a very low dropout regulator, and at that point the desing just become infeccienct. Instead we will use some kind of filter like a ferrite bead.

Power options:

Option 1: USB → 5V directly (more filtering involved, but have it on hand, less complex)
Option 2: USB → LDO →5V (optional for cleaner 5V, on hand, but tough to find LDO)
Option 3: Wall adapter → Switching regulator (quietest supply, standard, too complex and dont have a wall adapter on hand)
option 4: Bench supply at 5V (best for testing with low noise and adjustable, but no equipment needed)

Add-ons:

LED power indicator
TVS diode for ESD protection: unidirectional, single channel, working voltage should be 5V or more, need to design LDO before figuring out clamping voltage, capacitance is not critical, and high IEC rating preferred.

Total current draw requirements

VCO: 25mA
LED: 10mA
Op-Amp(maybe or for future use): 2mA
Margin: 5mA
Total: 42mA → about 50mA
Need to choose 50-100mA

Final choice:

150mA because its safe, more standard, and more readily available.

Final choice of LDO

This is how I found the LDO for the for mark 1 of this design, but I scrapped it because it was not necessary for USB power. But for the wall adapter, I thought it was necessary. I needed to pick a 5V-5V LDO