TriQuint Semiconductor, Inc. introduced the TQ5M31, a general purpose mixer/downconverter RFIC designed for multiple applications. These include mobile phone, CDPD, ISM, SatCom and WLAN data networks. The small size and excellent performance of the TQ5M31 make it usable for any application in the RF frequency range from 500 to 2500 MHz and with an IF output range of 45 to 500 MHz. The RFIC uses minimal off-chip matching components while maintaining maximum applications flexibility and high output Third Order Intercept efficiency. Small current drain, small physical size, and low cost make this part ideal for portable, battery operated applications.

The TQ5M31 configuration provides a buffered local oscillator (LO) input, a GaAs MESFET mixer, and an IF output amplifier all integrated in a single, small RFIC. Simple external circuits with minimum parts count are used to optimize: 1) the LO buffer amplifier frequency response to minimize mixer noise injection and 2) the IF gain response for optimum gain and intercept point for the particular application.

"The ability to optimize the performance of the mixer by varying a few external components makes the TQ5M31 ideal for hand-held applications where small size, low current consumption, and high performance are necessary" said Cathy Arb, Product Marketing Engineer for TriQuintęs Mixer Products.

Performance

The TQ5M31 conversion gain is 2.0 to 3.5 dB depending upon band of interest and varies by only +/-0.3 dB over the full operating temperature range. Input third order intercept point is 9.0 dB minimum (10 dB typical) with an associated noise figure of 9.5 dB. Isolations of 33 dB (RF to IF) and 40 dB (LO to IF) are demonstrated on standardized test boards. Performance can be optimized by tuning three circuit elements: the LO buffer amp bias port; the IF output port; and the GIC (Gain/Intercept/Current) port.

The output of the LO buffer amplifier can be tuned with a single inductor to optimize out-of-band noise power. The Mixer IF output port impedance can be optimized for various filter and IF amplifier topologies with a simple series and shunt capacitor combination. Access to the "GIC" pin allows optimization of the Gain, Third Order Intercept, and Power Supply Current for a variety of wireless applications by controlling the current through the IF amplifier.

IF and LO input port return losses are greater than 10 dB. Leakage and unwanted mixing products are minimized by having the input port matched to 50 ohms over the entire RF frequency range. The LO input port is RF coupled and is internally matched to 50 ohms. This simplifies the design and keeps the number of external components to a minimum. The TQ5M31 operates from a single 2.8 VDC nominal supply and draws between 4 and 7 milliamps depending upon application and bias current.

Applications

The approach of utilizing an LNA RFIC, which is separate from the Mixer IC, improves system performance by providing better isolation and a lower sensitivity to filter matching.

The TQ5M31 offers a new level of performance with features well suited for the growing number of applications in the 500 to 2500 MHz frequency range. Such applications include

WLAN, ISM, GPS, and L-Band Satcom transceivers in addition to phone handset applications operating in CDMA, TDMA, AMPS, or PCS modes and frequencies. The simple design and small size of the TQ5M31 mixer/downconverter with the aforementioned specification "tuneability" allow it to replace discrete device realizations without sacrificing performance or power consumption.

A typical example of achievable performance with optimization is for a PCS application. When operated at a supply voltage of 2.8 Volts the IC draws about 6 mA. With an RF input frequency of 1960 MHz, an LO frequency of 1750 (low side), and an IF frequency of 210 MHz, the TQ5M31 provides a conversion gain of 3 dB with an associated noise figure of 9.5 dB and input third order intercept point of +10 dBm. LO drive level is ę4 dBm for the above performance, although satisfactory performance is obtained with LO drives in the ę7 to 0 dBm range.

This is one heck of a nice drop-in part which I can see being configured into any number of applications. I like particularly the 2.8-V operation, the adjustable gain and high, adjustable IP3, the low current and the broadband performance. I don't much care for the 9.5 dB noise figure which kind of forces you into using an LNA -- even if the signal levels might not have fully warranted it -- and the RF input return loss is only 10 dB, helping even more to justify a front end amplifier; but most users would have planned it that way anyhow. The IF output uses an open-drain configuration to help with the wide frequencies possible with different external filter impedances although, typically, a narrow band SAW or crystal filter will offer impedances from 300 to 1000 ohms with about 2 pF of capacitance.

Like the RF input the LO input has an internal dc blocking capacitor and a reasonable return loss (10 dB, again) so that a VCO can be connected directly into the port on a 50 ohm line with no other components. Most applications would require nine external components, only two of those being inductors (2.2 and 39 nH), and with no variable components. In the 6-pin SOT-23 package it should be possible to build the complete converter on a PCB area of about 10 square mm; it should also be kept in mind that this part is an ideal starting block for a multi-band receiver.

TriQuint will do extremely well with this part. The TQ5M31 is sampling now and is priced at $2.08 in 1000-piece lots.