I have designed a PCB board, having a RF power amplifier with an output power of 34dBm and two voltage regulators giving output voltage of 2.7V and 3.5V respectively which will be the input to power amplifier.
How to measure the output power of this PCB board after assembling the components? or Is it possible to measure the output power before assembling ?
Electrical – How to measure the RF output power of the PCB board
pcbpower amplifierRF
Related Solutions
You add up the current draw of all the components, and then make sure the power supply can handle it. Note that you want to add up the worst case current draw to be sure it will always work over all conditions the parts are specified for.
If this is a high volume product where reliability in extreme conditions is not that important, then you can use some fudge factor to size the power supply somewhere between the max current for all components and their typical values. The more components there are, the lower the probability that they will all draw their maximum current at once. These need to be different components for this statistical analysis to be valid. Dirty Harry summed up this method well: "Do you feel lucky? Well do you, punk?".
No, this is generally not possible because of the rest of the circuit. If you have a schematic you may be able to analyze the circuit and figure out what the value is from the 'incorrect' reading, but that is not always possible, even under ideal conditions. By ideal, I mean that you have a perfect understanding of the circuit, how you measuring instruments work (for example the waveforms used to measure capacitance including the voltages on each range) and how parts such as the chips Nick mentions behave when not powered and subjected to those waveforms). If a much smaller and/or less accurate part is effectively in parallel it may be impossible to get an accurate number.
The most reliable way is to remove the parts with a tweezer type desoldering tool and measure it, then replace. Some larger (0603 and up) resistors are still marked but there are many smaller resistors and most SMT capacitors that are not marked at all (photo from here).
Related Topic
- Electronic – How to measure the impedance of PCB trace
- Electronic – Ensuring certain amplitude level of RF signal on a PCB board
- Electronic – Which components can be measured while soldered on a PCB board already
- Electronic – Testing process before PCB assembly
- Electronic – How to go about debugging PCB Power Supply Circuits to ensure correct output voltage
Best Answer
The most correct way to measure RF power is with an RF power meter. These come in various shapes and sizes from vendors like Keysight, Rohde & Schwaz, etc. The tricky part here is that you might not have a clean, intended output point to measure from (if your antenna is integrated on the same PCB).
These devices need to be calibrated in order to make the measurement.
Alternatively, you can use a device like a spectrum analyzer to measure the output power. This will however not give you quite the same accuracy, and can also not be calibrated as easily to take into account cable losses. However, at 800-something MHz that you are working at, cable losses will not be too significant (it all depends on quite how accurate you need to measure this).
If you need to measure the power while the device is running, you can use power meter IC's. These are common as they are used for RSSI measurements, gain control, etc. Some out there are able to measure to sub-0.1 dB accuracy.