A Complete MMIC Chip Set for 38 and 42 GHz Applications

Avago Technologies' five-chip monolithic microwave integrated circuit (MMIC) solution, shown in Figure 1, targets the expanding 38 and 42 GHz point-to-point radio markets. This solution enables the end user to source a complete RF front-end solution from a single supplier allowing for fast time-to-market. Avago designs millimeter-wave products in high-performance 5 × 5 surface-mount technology (SMT) packages to enable a robust and automated manufacturing flow.

Point-to-Point Wireless Markets

The wireless infrastructure market is expanding to meet the increasing demands of cellular customers. Smart phones and tablets are driving an ever-increasing amount of data that must be handled by backhaul networks. Point-to-point microwave is one of the main methods of backhaul deployment around the world besides copper T1/E1, Ethernet over fiber and Ethernet over copper. Microwave is the primary method of backhaul in Asia-Pacific, Western Europe, the Middle East and Africa.

In the areas of the world where 38 GHz (37 to 40 GHz) microwave backhaul is deployed, the network is already approaching capacity issues. Network operators are therefore looking to overlay 42 GHz (40.5 to 43.5 GHz) as a new microwave band to provide extra high-capacity short haul radio links. Packaging can pose a key difficulty in providing a robust manufacturable RF solution at 42 GHz where traditional plastic lead-frame solutions no longer work effectively. In this application, Avago's fully matched, air cavity laminate 5 × 5 mm package offers an advantage for achieving high performance.

Manufacturing Capacity and Chip Set Description

The MMIC designs are fabricated using Avago's proprietary 0.17 micron gate Pseudomorphic High Electron Mobility Transistor (PHEMT) process. With >80 GHz FT transistors, this process is more than capable of meeting the applications at 40 GHz frequencies. Manufactured in Avago's high-yield, high-volume, 6-inch wafer processing facility, the primary chips are packaged in 5 × 5 mm SMT packages (see Figure 2). The manufacturing and test operation is fully automated and capable of supplying millions of chips per month.

AMGP-6551 Up-converter/VGA

The AMGP-6551 uses a balanced sub-harmonic approach to reduce local oscillator (LO) leakage that may appear on the RF signal, thus easing filter requirements. Based on a single balanced SH-SSB mixer followed by an amplifier-attenuator-amplifier-attenuator-amplifier, it features low-noise figure, good linearity, conversion gain and gain control.

High input linearity is achieved by distributing gain and loss stages so none are saturated. Low distortion is achieved by having the attenuator FET never enter the nonlinear range. This is done by employing a "lossy-line" approach that sequentially adds more and more loss to the signal as the shunt FET is turned on, but without ever getting close to the nonlinear pinch-off region.

Over the 37 to 44 GHz range, the AMGP-6551 provides 12 dB typical up-conversion gain with 24 dB of gain control. 50 Ω RF/LO match is achieved at all ports and the typical output third-order intercept point is +17 dBm. The AMGP-6551 is housed in a 5 × 5 mm SMT package and operates from a 5 V supply, drawing 300 mA typical.

AMGP-6552 Down-converter

The down-converter consists of a four-stage low noise amplifier (LNA) combined with a sub-harmonic pumped image rejection mixer. The LNA is fed into an RF in-phase power divider in the mixer. From the power divider the signals are fed into one side of anti-parallel diode pairs to produce sub-harmonic pumping. The other side of the anti-parallel is pumped from a LO split using a Lange coupler. A LO buffer amplifier is not used since unwanted second harmonics can easily be produced here and self-mix down to near the intermediate frequency (IF). Over the frequency range it provides 14 dB typical down-conversion gain. Typical noise figure of 4.5 dB is achieved and typical input IP3 is -5 dBm.

AMGP-6445 Power Amplifier

The AMGP-6445 MMIC linear power amplifier (PA) is a four-stage design with three separate gate and drain supplies for optimum bias. It is designed for transmitters that operate between 40 and 44 GHz. In the operational band, it provides typical 29 dBm of output power (P-1dB) and 21 dB of small-signal gain. The AMGP-6445 device is also designed for high linearity applications, and the PA shows typical +35 dBm OIP3.

The input, inter-stage and output matching circuits are composed of pre-matching circuits and impedance transformers. The final power combiner is critical to phase-match eight separate FETs to combine the total power into one cohesive output.

AMMP-6125 LO Buffer with Frequency Multiplier

The AMMP-6125 local oscillator is an easy-to-use integrated frequency multiplier (× 2) in a surface-mount package. The MMIC takes a 5 to 13 GHz input signal and doubles it to 10 to 26 GHz. It has integrated amplification, matching, harmonic suppression and bias networks. The input/output are matched to 50 Ω and fully DC blocked. The frequency multiplier is a differential amplifier that acts as an active balun. The outputs are connected so that even drain currents are in phase and thus add power, and odd harmonics are out of phase and thus suppressed.

AMGP-6342 Variable Gain Amplifier (VGA)

The VGA uses an attenuator-amplifier topology to maximize linearity, gain and gain control in a 5 × 5 mm SMT package. Suitable for 27 to 44 GHz applications, small-signal gain is 9 dB typical (37 to 44 GHz) and gain dynamic range is 35 dB typical. Operating from a 5 V supply current draw is 205 mA typical.

VMMK-3413 Power Detector

The power amplifier includes a simple built-in resistive power detector, as most power amplifiers do, and it is useful for a gross "on or off" system level power detection; however, since it is resistive, it has only limited range and no directivity. Many modern forward-correction systems require knowledge of the actual power being transmitted independent of antenna load. The Avago directional temperature compensated power detector is suitable for handling these types of applications. The VMMK-3413 detector uses a very high tolerance coupler combined with a DC differential amplifier connected to an internal diode reference. A wafer-scale package is used for low cost and for small size (0.5 × 1.0 mm).

The detector's insertion loss is only 0.8 dB typical in the 42 GHz band. The detect voltage is 0 to 3 V over a -5 to +25 dBm power range. The 8 dB directivity allows true transmit power measurement compared to resistive power detectors that have no isolation from reflections. Operating from 1.5 V, current draw is typically only 0.15 mA.

Conclusion

A performance summary for the chip set is shown in Table 1. The MMIC family allows designers to source a complete 38 to 42 GHz radio solution in surface-mount technology from one vendor for better quality control, application support and shorter time to market.

Avago Technologies Inc.,
San Jose, CA
(877) 673-9442,
www.avagotech.com