433mhz saw filter: Selection Guide and Key Specifications

Basic Principle of Surface Acoustic Wave Filter

The English abbreviation of surface acoustic wave filter is SAW, and the full name is Surface Acoustic Wave. It is different from an ordinary filter built with discrete inductors and capacitors. It allows sound waves to complete frequency selection on the surface of a piezoelectric material. The interdigital transducer at the input end first converts the radio frequency voltage into an acoustic wave propagating along the surface of the material. After the acoustic wave propagates and interferes, the interdigital transducer at the output end turns back to an electrical signal. The period of the interdigital electrode and the speed of sound on the surface of the material together determine the main operating frequency of the device, while the piezoelectric material, aperture, number of fingers and reflection structure together affect the bandwidth, loss and suppression. Because the frequency is mainly determined by the geometric size of the electrodes, such devices can make a very high selectivity in a small volume, and the consistency in mass production is also very good.

Why is 433 MHz so common?

The frequency point of 433 MHz, especially 433.92 MHz, is particularly frequent in short-range wireless scenarios such as remote control, telemetry and IoT front-end. It has low cost, low power consumption, and does not require complex networking. Many remote control devices and wireless sensors are used. For this reason, the 1 433mhz saw filter is often used as the first 1 checkpoint at the front end of the receiver, suppressing out-of-band interference and retaining only the required signals. When selecting 433 mhz saw filter, the first thing to check is often the center frequency: some materials fall at 433.92 MHz and some fall at 433.42 MHz, which may not match your system by one word.

Selection to see a few key indicators

Outside of the center frequency, the bandwidth is the second place where it is easy to step on the pit. The same 433.92 MHz surface acoustic wave filter, the bandwidth can vary from a few tenths of MHz to several MHz. The narrow bandwidth is suitable for narrowband telemetry or only a very narrow signal, while the wide bandwidth is more suitable for carrying a slightly wider modulation signal. Insertion loss indicates how much the signal is eaten after passing through the filter, the lower the better, but it is weighed in combination with bandwidth and suppression. Return loss and standing wave ratio reflect port matching. If the matching is not good, the previous indicators will be discounted. Another point is easily overlooked: the stopband suppression must fall on a specific frequency band, and a single deepest notch point does not mean that the entire stopband is suppressed.

Package and Port

The package determines how the device is mounted and grounded. Common packages include QCC8 and DCC6, which are small in size and suitable for reflow soldering. In terms of ports, attention should be paid to whether it is single-ended or differential: single-ended structure is simple, directly to 50 ohm system; Differential structure can suppress part of common mode interference, but impedance, matching and grounding should be checked according to differential caliber. Nominal impedance, static level and maximum input power are usually also noted on the data sheet, which should not be skipped. The maximum input power of the SAW device may be given by continuous wave, peak or lifetime average power, with different calibers and no direct comparison between numbers.

boundary of temperature and power

Surface acoustic wave devices have a physical characteristic that cannot be wound: if the temperature changes, the center frequency will drift. The passband measured well at room temperature will shift as a whole in high or low temperature environment, so the design margin should take this drift into account. If the system is particularly sensitive to temperature, temperature-compensated surface acoustic wave technology can be considered, which presses down the frequency temperature coefficient through materials, coatings, or composite structures, at the expense of usually a little change in insertion loss, bandwidth, or process complexity. In terms of power, the same boundary should be left. After all, the surface acoustic wave filter is an acoustic device and is not used to carry high power. When selecting the type, the maximum input power and temperature derating should be confirmed.

Practical Application Scenarios

In products such as remote control equipment, remote telemetry and sensor nodes, the 433 MHz SAW filter plays the same role: the unnecessary frequency band is blocked at the front end of the receiving link, so that the low noise amplifier and subsequent circuits behind only face clean signals. Understand its principle, and then compare the data table to see the center frequency, bandwidth, insertion loss, package and power boundary one by one, choose the 1 appropriate 433 MHz surface acoustic wave filter, it is much more reliable than simply staring at the center frequency.