Fig 1. This direct conversion RF transmitter from CFTL Circuits Notes CN134 covers from 500 MHz to 4.4 GHz and uses a standard ADI PLL chip called the ADF4350, a fractional or integer N PLL synthesizer for the local oscillator (LO). It also drives the ADL5375 quadrature modulator.
Fig 1. The CN134 evaluation board shows one of the 150 designs available to speed your design or help you learn something new.
Electronics engineers are being asked to design their products faster and with increasingly more complex technologies but with a shorter time-to-market. They are also being asked to do more with less and include cross-discipline technology for new markets. On top of that, they are now more than ever asked to design-in wireless features to enhance product differentiation and improve marketing. The faster designs are a problem, of course. But even worse, what EE knows anything about RF and wireless? Not many.
Engineers learn their discipline in college, and the EE curriculum includes more digital and computer stuff than analog. Very few engineers ever take an RF course other than perhaps a “fields” course featuring the ever popular Maxwell’s equations. This creates some serious shortcomings for engineers when they have to design mixed-signal products.
And what about those wireless features? Analog Devices (ADI) has been addressing this problem with its Circuits from the Lab (CFTL) program, which provides clear-cut design help to bail out those struggling with mixed-signal designs including wireless. Now, more RF and wireless designs are available.
These pre-designed standard circuits use ADI parts and include full schematics, bills of materials (BOMs), layout files, test data, device drivers, and other essentials. Such a package can help engineers save weeks of research and design time. Furthermore, these tested designs can better ensure a workable, repeatable, and reliable design with fewer board spins. This means fewer trial and error iterations of the design and fewer dead end explorations.
A good example of a typical RF design is a direct conversion RF transmitter such as this one from CFTL Circuits Notes CN134 (Fig. 1). This transmitter covers from 500 MHz to 4.4 GHz. It uses a standard ADI phase lock loop (PLL) chip called the ADF4350, a fractional or integer N PLL synthesizer for the local oscillator (LO).
The design drives the ADL5375 quadrature modulator. Its on-chip 90°splitter delivers the LO to the mixer/modulator circuits. Note that the I and Q inputs are provided. The design even includes critical circuits like the low-pass filter between the PLL LO and the modulator. Often, interface circuits like this take up more design time than expected.
The CFTL designs are a good way to implement a design that may not usually be in your sphere of knowledge. So, take a look at some of the 150 designs now available to speed your design or just to help you learn something new (Fig. 2).
Analog Devices Inc.
www.analog.com/circuits