MEMS switches that KO conventional switches are excellent for use in these circuits
Microelectromechanical systems (MEMS) switches have long been touted as an excellent replacement for the limited performance of electromechanical relays because they are easy to use, small in size, and can reliably transmit signals from 0 Hz/dc to hundreds of GHz with minimal losses, promising to revolutionize the way electronic systems are implemented.
ADI's MEMS switch technology enables leapfrog advancements in RF and DC switching performance, reliability, and miniaturization compared to traditional electromechanical relays.
Take the ADGM1304, ADI's broadband, single-pole, four-throw (SP4T) switch, for example. This product is manufactured using ADI's MEMS switch technology, which enables high-power, low-loss, low-distortion GHz switching required for demanding RF applications.
The figure below is a cross-sectional schematic of the switch. It is an electrostatically actuated cantilever beam switch in a three-terminal configuration. It is similar in function to a field effect transistor (FET) with the terminals acting as source, gate, and drain.
Cross section of a MEMS switch design showing the cantilever switch beam (not to scale)
-
Unlike other switch alternatives such as solid-state relays, the ADGM1304 offers excellent accuracy and RF performance from 0 Hz (DC) to 14 GHz.
-
The highly reliable ADGM1304 improves cold switch life by 10 times compared to electromechanical relays, extending ATE system operating life and reducing costly downtime due to relay failures.
-
Compared to DPDT relay designs, the integrated charge pump eliminates the need for an external driver, further reducing ATE system size, while the multiplexer configuration also simplifies the fan-out structure.
No matter who you compare it with, the MEMS switch ADGM1304 is "better". So, in which circuits is this "unrivaled" MEMS switch better applied? The official suggestion given by ADI is:
Switchable RF Attenuator
RF attenuator networks are commonly used in RF instrumentation equipment such as vector network analyzers, spectrum analyzers, and signal generators. Routing RF signals through attenuators allows the equipment to accept higher power signals, thereby increasing the dynamic range of the instrument. In RF attenuation applications such as vector network analyzers, spectrum analyzers, and signal generators, it is critical to maintain the bandwidth of the signal after it passes through the network. Degradation of the signal can reduce the performance of the equipment. Therefore, the RF characteristics of the switches used for routing are an important part of the attenuator network.
The ADGM1304 MEMS switch has low and flat insertion loss, ultra-wide RF bandwidth, and high reliability, making it suitable for use as a switchable RF attenuator. The ADGM1304 also provides additional flexibility as an SP4T switch. Figure 1 shows an example of an attenuator network configuration using two ADGM1304 switches and three different attenuators. The fourth channel of the switch is used for the non-attenuated routing in Figure 1.
Figure 1. Switched RF attenuator using the ADGM1304 MEMS switch.
Reconfigurable RF Filters
Reconfigurable RF filters are very beneficial for many RF front-end applications. It can save more space. As the space of applications becomes more and more limited, cost-effective and easy-to-use reconfigurable RF filters are undoubtedly more attractive than multiple frequency-dependent filters.
To switch on the lumped elements (capacitors, inductors), the ADGM1304 MEMS switch is required, which features very low and flat insertion loss, ultra-wide RF bandwidth, low parasitics, low capacitance, and high linearity, making it ideal for reconfigurable filter applications.
In applications such as wireless communications or mobile radio, the number of frequency bands and/or modes is increasing. With reconfigurable RF filters, more bands/modes can be supported by the same component.
An example of a reconfigurable bandpass filter is shown in Figure 2. The topology shown is a generalized two-section, inductively coupled, single-ended bandpass filter with a nominal center frequency of 400 MHz (UHF band). Note that a MEMS switch is placed in series with each shunt inductor.
Figure 2. Reconfigurable band-pass filter implemented using two ADGM1304 MEMS switches.
The switch is used to include or exclude the shunt inductor from the circuit. Changing the shunt inductor value affects the bandwidth and center frequency of the filter. Using inductor values from 15 nH to 30 nH significantly changes the bandwidth and center frequency, allowing the filter to be dynamically configured to operate in the ultra-high frequency (UHF) or very high frequency (VHF) bands while retaining a 50 Ω match at the input and output ports.
The low RON and wide bandwidth of MEMS switches make them ideal for such applications -
-
Low RON reduces the adverse effect of series resistance on the shunt inductor quality factor
-
Large bandwidth enables implementation of higher frequency bandpass filters
京公网安备 11010802033920号