Development Kits Let Designers Check out Single Components to Systems-on-a-Chip for Wireless Designs

Whether you need to check out a new embedded antenna, an antenna switch, RF power amplifier, or a more complex amplifier, evaluation boards and development kits from the component vendors provide a quick and low-cost way to evaluate various options or create a proof-of-concept solution before committing to a full design. The range of choices can also meet the demands of tight budgets, therefore keeping development costs as low as possible. With the evaluation boards, you can implement a full wireless system signal chain, from the antenna to the transceiver, and even link that subsystem to the host system.

Low-cost evaluation boards are often fairly minimal subsystems and are typically small boards with the component mounted and a few connectors for power and signal inputs and outputs. Some boards also include a small prototyping area to allow designers to customize their solutions. This is true especially for the more complex circuits on development boards. Such boards tend to offer many options to give designers a lot of flexibility in developing their solutions.

Let us look at some of the evaluation/development kit options for the wireless signal path from the antenna to the transceiver. Even simple passive devices such as embeddable antennas deserve evaluation boards to better determine how the antenna might react in the system in which it will be used. Antenova, Ethertronics, Laird, Pulse Finland, and Taoglas all offer simple development board for their antennas. The Mica 2.4 GHz SMD antenna from Antenova targets Bluetooth, Wi-Fi, and ZigBee, as well as WiMAX at 2.3 and 2.5 GHz and WiBro. A simple evaluation board with proper ground plane under the antenna lets the antenna deliver an optimum radiation pattern (Figure 1a). Ethertronics offers several evaluation options, the Savvi is an embedded ceramic antenna targeted at wireless LANs for 802.11a/b/g applications in the 2.4 to 2.5 and 4.9 to 5.8 GHz bands (Figure 1b, left), while the Prestta is a standard penta-band embedded antenna for cellular systems on frequency bands of 850/9001800/1900/2100 MHz (Figure 1b, right). Both evaluation boards are simple designs just consisting of the antenna mounted on a ground plane and a small RF connector to connect to the rest of the system. Both antennas use the company’s isolated magnetic-dipole technology that helps keep the antenna size small and minimizes detuning regardless of the usage position.

Taking aim at Bluetooth and 802.11 applications the BlackChip™ surface-mount antennas from Laird Technology come in small surface-mount packages that are mounted on a small printed circuit board (Figure 1c). The antenna can work over frequency bands of 2.4 to 2.5 GHz, 5.5 to 5.35 GHz, and 5.7 GHz. For global positioning systems that operate at 1,575 GHz, two compact antennas, one from Pulse Finland and the other from Taoglas, offer dimensions of 10 x 3.2 x 4 mm and 25 x 25 x 4 mm. Although not shown to scale, the Pulse antenna on the company’s evaluation board (Figure 1d, left) consumes less than half the area of the Taoglas antenna (Figure 1d, right).

Figure 1: Antenna evaluation boards have relatively simple designs as these boards from Antenova (a), Ethertronics (left – Savvi, right – Prestta), Laird (c), and Pulse Electronics (d) all show.

Signals between the antenna and the rest of the system are usually routed through a switch that provides band selection for multiband antennas, or between different radios in a wireless system. The µPD5902T7K is a CMOS high-power SPDT (single-pole double-throw) switch targeted at GSM and UMTS/LTE main antenna switching for power levels of up to +35 dBm. The chip, from CEL, comes mounted on a simple circuit board that has three RF connectors and several power pins (Figure 2a). Offering multiple switch options, Peregrine Semiconductor leverages its UltraCMOS process to produce SPDT switches such as the PE43742 for the CATV, digital TV, multi-tuner DVR, set-top-box, and game console markets, and markets the PR42430 SP3T RF switch for wireless LAN and Bluetooth, which spans the 0.1 to 3 GHz frequency range (Figure 2b, left and Figure 2b, right).

Figure 2: The RF switches pictured here are the SPDT circuit from CEL (a), the SPDT switch from Peregrine Semiconductor (b, left), the company’s SP3T switch (b, right), the Skyworks HEMT-based switches that handle 20 MHz to 2.5 GHz in a SPDT configuration (c, left) and the DPDT version with a bandwidth of 100 MHz to 6 GHz (c, right).

To handle higher-power applications, switch circuits implemented using p-channel HEMT (high-electron-mobility transistor) devices in gallium arsenide can handle 10 W over a frequency band of 20 MHz to 2.5 GHz. One such offering, the SKY13290-313LF from Skyworks Solutions comes in a SPDT configuration and is housed in a tiny, 2 x 3 mm, 6-contact, quad flat package that is mounted on a small circuit board for evaluation (Figure 2c, left). Another pHEMT offering from the company, the SKY13355-374LF, operates over a 0.1 to 6 GHz band and comes in a DPDT configuration. The tiny, 1.5 mm² surface-mount package is almost invisible when mounted in the center of the evaluation board (Figure 2c, right).

As part of the signal path, digital attenuators are often inserted to control the signal strength. One such device offered by Honeywell, the HRF-AT4610, can operate over a DC to 4 GHz range and uses a 6-bit digital control code to attenuate the signal in steps from 0.5 to 31.5 dB. Implemented in a silicon-on-insulator CMOS process, the attenuator has an insertion loss of just 2.5 dB at 1 GHz and 3 dB at 2.5 GHz. The evaluation board from Honeywell is a simple design with the chip at the center and the digital input and power supply connections running along the top of the board (Figure 3).

Figure 3: A digitally-controlled attenuator, the Honeywell HRF-AT4610, uses a 6-bit input to control the attenuation from 0.5 to 31.5 dB in 0.5 dB steps.

Going further down into the signal chain, the next blocks you will typically encounter are power amplifiers on the transmit side, and low-noise and basic amplifiers on the receive side. Targeting the cellular infrastructure, two-way private radios, and broadband amplifiers, RF power transistors such as the CGH40006 from Cree come in either a ceramic or plastic surface-mount package. The HEMT device is fabricated in gallium nitride (GaN) for high efficiency and delivers 13 dB of small signal gain at 2 GHz and 11 dB at 6 GHz. The evaluation board offered by Cree provides a basic power-amplifier layout with the transistor supported with the necessary biasing and bypass components, and the 3 x 3 mm package located dead-center between the input and output ports (Figure 4a).

Complete power amplifiers in a package are available from Hittite Microwave. The HMC580ST89 MMIC is based on Indium Gallium Phosphide heterojunction bipolar transistors (InGaP HBT) and has a bandwidth of DC to 1 GHz, delivering a gain of 22 dB. The evaluation board for this device has a simple layout with the amplifier centered between the input and output connectors and the layout optimized for 900 MHz operation (Figure 4b). On the receive side of the signal chain, or as a driver for the output stage, the Hittite low-noise amplifier (LNA), the HMC564LC4 MMIC, targets the 7 to 14 GHz band in point-to-point radios, military and space, and other applications. Based on pHEMT GaAs devices, the amplifier has a noise figure of just 1.8 dB typ and a small signal gain of 17 dB over the 7 to 14 GHz frequency range. The evaluation board has large ground planes and stripline connections between the amplifier and the input and output ports (Figure 4c).

Figure 4: Power amplifiers require large ground planes and good heatsinking as the evaluation boards from Cree (a), Hittite Microwave (b), Hittite low-noise amplifier (c), and a power amplifier from RFMD (d) all illustrate.

Implemented using GaN HEMT devices, the RFHA1000 and RF3931 power amplifiers from RFMD deliver 15 and 30 W. The RFHA1000 can operate over a 50 MHz to 1 GHz band, while the RF3931 offers a wider, DC to 3.5 GHz operating bandwidth. Another amplifier, the NBB-400 has DC to 8 GHz bandwidth and gets the wide bandwidth by combining InGaP HBTs and GaAs HEMTs to craft a MMIC amplifier that delivers 15 dB of gain at 2 GHz and 14.6 dB at 6 GHz. Evaluation boards for the amplifier mount the device dead-center between the input and output ports and heavy ground planes to provide shielding and matched impedances for the amplifier’s input and output (Figure 4d).

For more complex circuits, still larger development board and evaluation kits are available to check out functions such as downconversion mixers, logarithmic detectors, ISM band transceivers, and many other functions. A future article will examine some of the development board options for these circuit functions.