The SIM-U432H+ mixer accepts intermediate-frequency (IF) signals from 260 MHz to 460 MHz and local oscillator (LO) signals from 2550 MHz to 4250 MHz at a nominal level of +17 dBm to produce RF output signals from 2200 MHz to 3900 MHz (well in excess of the WiMAX band range). It performs the frequency upconversion with typical conversion loss of 7.5 dB (Table 1). The mixer's conversion loss is well behaved with frequency even at other LO drive levels. For example, the SIM-U432H+ was tested with LO drive levels of +14 dBm, +17 dBm and +20 dBm and exhibited consistent conversion-loss profiles across the 2200 MHz to 3900 MHz RF output range (Figure 3). Performing swept-frequency testing at different LO drive levels simulates the effects of variations in LO power from unit to unit as well as across wide frequency ranges. The variation with LO drive power is typically +1.5 dB/-0.5 dB across the 1700 MHz measured bandwidth.

The integrity of the mixer's circuit design is most evident in the port-to-port isolation. High isolation is instrumental in achieving good performance in dual-mixer in-phase (I) and quadrature (Q) modulators. Also, a mixer with high isolation requires less additional external filtering to reduce unwanted signal content, such as LO feedthrough. The LO-to-RF isolation of the SIM-U432H+ mixer was also evaluated at the three LO drive levels used for the conversion-loss tests, to compare performance at different LO levels and to understand the effects of variations in LO power on isolation. As Figure 4 shows, the LO-to-RF isolation is high (typically 33 dB) and well behaved at all three LO drive levels. Variations in isolation as a function of LO power are typically ±2 dB.

Similarly, the LO-to-IF port isolation was evaluated at the three LO drive levels. While isolation between these two ports is less critical in an upconverter applications (where a greater concern is feedthrough of LO signals to the RF output port), the SIM-U432H+ mixer nonetheless exhibited typically 26 dB across a LO frequency range of 2550 MHz to 4250 MHz (Figure 5).

Since wide dynamic range is important in many WiMAX-band applications, the input third-order intercept point (IP3) of the SIM-U432H+ mixer was also evaluated at the three LO drive levels (+14 dBm, +17 dBm and +20 dBm) and an RF output range of 2200 MHz to 3900 MHz. The mixer's input IP3 is consistently about +26 dBm across most of that range for the output (Figure 6).

The LTCC double-balanced mixer features typical LO port return loss of 12 dB. The return loss measured at the RF port is 10 dB typical in the WiMAX band of frequencies while the return loss at the IF port is typically 10 dB to 15 dB across the full IF band.

For WiMAX applications the SIM-U432H+ double-balanced mixer provides an extremely compact, high-performance solution based on a stable LTCC process. The mixer supports conventional surface-mount applications, and can be supplied in tape and reel formats for use with automated assembly equipment. The RoHS-compliant mixer fills a range of global WiMAX applications and is designed to withstand high levels of ESD mishandling compared to more sensitive, and larger, semiconductor mixers.

1. Mobile WiMAX — Part I: A Technical Overview and Performance Evaluation, WiMAX Forum, par. 7.3, http://www.WiMAXforum.org/news/downloads/Mobile_WiMAX_Part1_Overview_and_Performance.pdf.

2. United States Patent No. 7,027,795 (2006).

Radhakrishna Setty, Mini-Circuits, Brooklyn, NY.

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