A New Maxim Integrated Low-Power RF Transmitter for Automation, Wireless Sensors, and IoT Devices

Maxim has released the MAX41461, a highly integrated ASK transmitter that works in the sub-GHz ISM frequency bands and is intended for a variety of low-cost wireless applications.

Not too long ago, a colleague and I were discussing the design for an inexpensive, customizable RF transceiver that could be incorporated into a wide variety of applications that require low- or moderate-bandwidth transmission of digital data. We were considering the S2-LP from STMicroelectronics, which really does appear to be a high-performance device: operation in four different frequency bands, four modulation options, data rates up to 500 kbps, automatic gain control, real-time RSSI (received signal strength indication), and various other notable features.

If I’m determined to use the same IC for both transmission and reception, the S2-LP is probably a good choice. Another option is the CC1350 from Texas Instruments. This device is actually a “wireless microcontroller”—it is not only an RF transceiver but also a microcontroller built around an Arm Cortex-M3 processor.

However, for applications that don’t need to use a single chip for both Tx and Rx functionality, I recommend that you take a close look at a new transmitter IC from Maxim.

The MAX41461

One thing that I like about the MAX41461 is the simplicity.

The block diagram from the MAX41461 datasheet.

It doesn’t seem to be overloaded with features that I don’t need. It’s great that some parts provide a wide variety of sophisticated functionality, but an abundance of sophisticated functionality comes at a price. For one, there’s the ... well, the price. The MAX41461 sells for $0.65 in large quantities. The two parts discussed above are significantly more expensive.

The other issue is that advanced features often introduce additional complexity into the design process. Perhaps there are more pins, or more registers to configure, or multiple application circuits to consider, or stricter power supply requirements. As engineers we need to focus on parts that meet our requirements without exceeding them—excess functionality can easily become a burden.

Modulation

The MAX41461 transmits digital data using amplitude shift keying (ASK). The most basic type of amplitude shift keying, and actually the most basic type of digital modulation in general, is on-off keying (OOK). As the name implies, this consists of turning the carrier signal on and off in accordance with the digital data:

This is certainly not the most robust type of modulation, but the important point is that it is adequate in many applications. Again, we’re dealing here with the simplicity concept—in general, the simpler solution is better if it gets the job done.

However, if for some reason ASK is unacceptable in your operational environment, Maxim offers a pin-compatible part that uses frequency shift keying instead of amplitude shift keying.

Implementation

RF design is not exactly known for being straightforward, and if my goal is to get a functional product to market in a reasonable amount of time, I’ll be looking for a part that doesn’t require a lot of external components. The MAX41461 appears to require seven, along with a microcontroller for I2C register configuration.

The application circuit from the MAX41461 datasheet.

The section of the datasheet preceding this diagram provides detailed information on how to select the frequency of the crystal. Unfortunately, I didn’t see any guidelines on how to choose the values of the passive components. It’s possible that this information is available in a separate document, and I assume that the application engineers at Maxim would be willing to provide some personalized design assistance. Nevertheless, I like it when the datasheet includes at least a few paragraphs on power-supply decoupling, the output-matching network, and antenna selection.

Frequency Hopping

Despite the fact that the MAX41461 is designed for the low-cost market and doesn’t emphasize advanced features, it does support basic spread-spectrum functionality. Spread-spectrum techniques make an RF system more resistant to interference, both intentional (in which case it is called jamming) and unintentional.

The MAX41461 doesn’t directly implement spread-spectrum communication, but it does allow for it. More specifically, it allows for frequency-hopping spread-spectrum communication. As the name implies, frequency-hopping utilizes a carrier frequency that “hops” from one frequency to another. The MAX41461 is compatible with this technique because its integrated PLL has a fast response time.

If you’ve had success in the past with an integrated RF transceiver or transmitter, it would be great to hear about your experiences. Part recommendations are always appreciated!