Monolithic analog ICs are pushing higher and better into the gigahertz-range RF domain traditionally supplied by hybrid and modular devices built using assemblies of multiple parts. A combination of factors is making it feasible for them to effectively address this attractive market opportunity: advances in process technologies; the critical productivity offered by better modeling, layout, and simulation tools; and packaging enhancements which are compatible with the tiny die sizes.
As there are many essential RF functions such as mixers or oscillators which can only be implemented in the analog domain (usually established by the laws of physics), it is an opportunity for analog IC vendors to gain new markets and design-ins with smaller, lower-power, lower-cost device with comparable or superior performance. The challenge for IC vendors has always been that once the product die is cast – literally and figuratively – any changes are expensive and time-consuming, so getting a design right the first time is critical. In contrast, while hybrid and modular solution have a serious cost disadvantage compared to ICs, they have the flexibility of being able to more conveniently probe the product internally and change component values, placement, and even type if the first version does not function as intended.
Two somewhat overlapping products demonstrate both the trend and the capability of ICs in the GHz arena.
The first device, the ADRF6612 from Analog Devices Inc. (ADI), targets wideband receivers, multimode base stations, and picocells, as shown in Figure 1. It is a dual RF mixer and IF amplifier with an integral phase lock loop (PLL) and pair of voltage-controlled oscillators (VCOs), ADI said. It incorporates an innovative broadband square-wave-based local oscillator (LO) amplifier to yield extremely wide bandwidth of 700 MHz to 3 GHz. While it supports a single-ended input interface to simplify incorporation within a system, it uses double-balanced differential mixers cores internally for improved performance, according to the company.
The ADRF6612 from Analog Devices mixer/IF amplifier incorporates a large number of high-performance functional blocks, targeting wideband RF applications from 700 MHz to 3 GHz.
The LO can be injected on the low side or high side (different applications have preferences for technical and historical reasons) and can range between 200 MHz and 2.7 GHz, while the IF range is 40 to 500 MHz. It provides relatively high power-conversion gain of 9.0 dB, along with a single sideband (SSB) noise figure of 11.3 dB. Other critical RGF specifications include input IP3 of 30 dBm and input P1(db) of 10.6 dBm, ADI said.
Assessing and incorporating a device with this level of performance at these frequencies is a non-trivial task, so Analog Devices provides an evaluation board to simplify the challenge, save time, and minimize user frustration. The initial settings and functions of the IC are user-controlled via a standard SPI port interface, for conveniences and ease of use. The 7 mm × 7 mm, 48-lead LFCSP device is priced to perceived value, at $14.99 (1000s).
The second device, from Linear Technology Corp., is dubbed the LTC5551. The chip is a down-converting mixer with ultrahigh dynamic range which offers 2.4 dB conversion gain, as shown in Figure 2. This gain is in sharp contrast to passive mixers which typically have conversion loss, not gain, of 7 to 9 dB and thus need additional gain, while also suffering reduced dynamic range, Linear said. Target markets include multicarrier systems, advanced base stations and backhaul links, repeaters, and military radar and avionics.
Linear Technology's LTC5551 downconverting mixer for 300 MHz to 3.5 GHz operation features a desirable combination of extremely wide dynamic range, conversion gain, and high linearity.
Like the Analog Devices’ part, this IC has a very wide operating-frequency range; here, it is 300 MHz to 3.5 GHz, Linear said. Its integrated local oscillator requires only a modest 0 dBm drive, which simplifies circuitry while eliminating the need for a high-power external LO signal, which is a potential source of undesirable radiation which often requires additional filtering and even physical shielding, according to the company.
This high-linearity mixer boasts IIP3 of +36 dBm and a 9.7 dB noise figure, along with a high 1-dB compression point of +18 dBm. Integrated balun transformers further reduce cost and space while improving signal integrity. Although it is a low-power, 3.3 V device (204 mA), users can invoke an even- lower-power mode (142 mA) by trading off a slight reduction in IIP3 to +29.3 dBm. The 16-lead 4 × 4 mm QFN package ($7.25 each/1000s) not only reduces real-estate requirements, but it also minimizes board and layout parasitics which are major factors in a system being able to realize only substandard performance, compared to what a component is actually capable of providing, Linear said.
The performance of these ICs does not mean that the days of non-monolithic GHz RF components are over: Analog’s recent acquisition of Hittite is proof of that. However, it does mean that suppliers of modular and hybrid components will have to keep moving up the frequency spectrum, and also emphasize their ability to do custom or short production runs on a short cycle-time scale, something ICs are inherently not well suited to doing as a result of their design and fabrication technology.
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