Automatic impedance matching in RF design
Impedance (Z) matching is an essential part of most RF circuit design. Regardless of what you’re designing, getting as much power to a load is a top target. Impedances must be matched to transfer the maximum amount of signal power between stages. And in power amplifiers (PAs), impedance matching is critical to getting the maximum power to the final load and maintaining PA linearity. Impedance matching to an antenna in a receiver or transmitter is an essential process.
Some loads are constant; thus, a single fixed Z-matching circuit can be used. But in other applications, that final load may change, or the frequency of operation will change, meaning that a fixed Z-match circuit will not produce the desired results. For these applications, a variable matching network that you can adjust is needed. Better still is a variable and automatic Z-match circuit that adjusts itself to the immediate load or frequency conditions.
Auto Z matching is more common than you think. If you own a recent smartphone, you’re probably using an auto Z-match antenna tuner. However, there are other applications. Here’s a primer on this topic for your elucidation and cogitation.
AC grounding: essential, dangerous, or both?
Most electrical engineers learn early-on about the importance of what are referred to as circuit grounds. In many cases, whatever your problem, adding a ground or improving the one you have (meaning lower impedance) is a good thing that can’t hurt. That’s what circuit EEs have drilled into them as they work and debug bench circuits prototypes, and more, and learn to connect the analog ground to the digital ground at one point only to minimize unwanted ground-current flow and associated noise.
In most cases, such grounding does improve circuit performance, but as every experienced engineer knows, every rule has legitimate exceptions, and grounding is one of them. A large part of the confusion comes from the ambiguous and this sloppy terminology associated with that innocent-sounding seven-letter word.
Rechargeable batteries enable greener electronics
While batteries provide untethered power, enabling convenience, dependability, and mobility, environmental responsibility suggests that rechargeable batteries have the same benefits, but can save money while reducing the amount of waste. This article examines the benefits offered by rechargeable battery technology, enabling us to make life better.
There are some errors in the “Automatic impedance matching in RF design” article.
(1) “Impedances must be matched to transfer the maximum amount of signal power between stages. And in power amplifiers (PAs), impedance matching is critical to getting the maximum power to the final load and maintaining PA linearity.” The first sentence is only true under conditions which do not apply for most transmitters. Typical transmitters whose desired load impedances are 50 ohms do NOT have source impedances of 5o ohms. The antenna tuner transforms the load impedance to 50 ohms not because the transmitter’s source impedance is 50 ohms but because a 50 ohm load is what the transmitter wants to see for optimum behavior.
(2) In Figure 1(c), the first L network with capacitor in parallel with the load and inductor in series with the 50 ohm terminal requires the load impedance to be MORE than 50 ohms, not less. And the second one with the capacitor from 50 ohm terminal to ground and inductor in series with the load requires the load impedance to be LESS than 50 ohms, not more.
Interesting article in ARRL’s current QEX magazine, May/June 2021, underscores and explains point 1)!