Abstract: This application note presents alternate RF matching networks for the MAX2653 SiGe LNA, tuned for the GPS band (1575MHz center frequency). Performance metrics (supply current, forward gain, NF, IIP3, reverse isolation and input/output return loss) for both high and low gain modes, as well as 2.7V and 3.0V supplies are provided. For VCC = 2.7V, high-gain mode, this application provides 19.2dB Gain, 1.6dB NF, and -5.2dB IIP3 at 5.6mA supply current. The MAX2653 SiGe Low Noise Amplifier (LNA) is internally optimized for lowest noise performance in the US PCS (1930MHz to 1990MHz) and the European DCS (1805MHz to 1880MHz) receive bands. These LNAs offer a 20dB gain control step, externally adjustable gain and linearity (via single external resistor), 2.7V to 3.3V operation, and a 0.25µA shutdown mode. Maxim does not offer a stand-alone LNA for the GPS (1575MHz center) band that includes a gain-step, but re-tuning the MAX2653 to this lower band offers a excellent solution. These alternative matching values (Table 1) offer 0.5dB more gain, 0.1dB better noise figure, and 2dB better IIP3 - all for nearly identical supply current. For applications that do not require a gain step, Maxim offers the MAX2654 and MAX2655 SiGe GPS LNAs. They offer a bias current control (via external resistor) to set gain and linearity, a 0.1µA shutdown mode and integrated 50Ω output matching. Find the datasheet at http://www.maxim-ic.com/max2654 . Figure 1. MAX2653 EVKit, with new matching components (C2, L1, L3, C4). No 'hacking' of the PCB necessary. Figure 2. MAX2653 EVKit schematic, with new matching components for 1575MHz GPS band. Table 1. MAX2653 EVKit replacement components for re-tuning to 1575MHz GPS band. Designation Value Description C2 1.3pF shunt-C (to GND) matching component for LNA input0402 ceramic capacitor Murata GJ61555C1H1R3CB01B L1 3.9nH series-L matching component for LNA input0603 printed inductor Toko LL1608-FS series L3 3.3nH shunt-L (to VCC) matching component for LNA output0603 printed inductor Toko LL1608-FS series C4 0.75pF series-C matching component for LNA output0402 ceramic capacitor Murata GJ61555C1HR75CB01B After replacing the matching components on the EVKit, key performance metrics were re-tested at room temperature—Table 2 provides the results of the re-tuned MAX2653 bench testing. These values are referred to the EVKit SMA connectors; to get values referred to the output of the matching networks, assume approximately 0.2dB loss at each the output and the input. In this fashion, the NF of the circuit is actually about 1.57dB, gain is about 19.2dB, and so on. Additional Gain and NF data over frequency is provided in Table 3. Table 2. MAX2653 GPS performance summary. Results are referred to the EVKit SMA connector. Parameter Symbol Conditions Test Result Unit Supply Current ICC High Gain Mode VCC=2.7V 5.61 mA VCC=3.0V 5.62 Low Gain Mode VCC=2.7V 2.23 VCC=3.0V 2.24 Gain G High Gain Mode VCC=2.7V 19.0 mA VCC=3.0V 19.0 Low Gain Mode VCC=2.7V -2.3 VCC=3.0V -2.2 NF NF High Gain Mode VCC=2.7V 1.77 dB VCC=3.0V 1.79 Low Gain Mode VCC=2.7V 6.36 VCC=3.0V 6.37 Input 3rd-order Intercept IIP3 High Gain Mode VCC=2.7V -5.2 dBm VCC=3.0V -4.9 Low Gain Mode VCC=2.7V +0.2 VCC=3.0V +0.2 Reverse Isolation |S12| High Gain Mode VCC=2.7V -33.8 dB VCC=3.0V -33.6 Low Gain Mode VCC=2.7V -22.2 VCC=3.0V -22.3 Input Return Loss |S11| High Gain Mode VCC=2.7V -7.7 dB VCC=3.0V -7.7 Low Gain Mode VCC=2.7V -10.9 VCC=3.0V -11.0 Output Return Loss |S22| High Gain Mode VCC=2.7V -12.6 dB VCC=3.0V -12.5 Low Gain Mode VCC=2.7V -8.1 VCC=3.0V -8.2 Table 3. MAX2653 GPS gain and NF performance over frequency. Results are referred to the EVKit SMA connector. Frequency High-Gain Low-Gain VCC=2.7V VCC=3.0V VCC=2.7V VCC=3.0V Gain (dB) NF (dB) Gain (dB) NF (dB) Gain (dB) NF (dB) Gain (dB) NF (dB) 1400 15.4 1.71 15.3 1.69 -5.4 6.36 -5.5 6.32 1450 18.4 1.74 18.4 1.74 -2.9 7.18 -2.9 7.40 1500 18.6 1.75 18.5 1.77 -2.6 6.45 -2.6 6.59 1550 18.6 1.78 18.6 1.75 -2.9 5.70 -2.7 5.51 1575 19.0 1.77 19.0 1.79 -2.3 6.36 -2.2 6.37 1650 18.7 1.86 18.7 1.82 -2.2 6.67 -2.3 6.66 1700 17.3 1.84 17.4 1.87 -3.5 5.64 -3.5 5.56 1750 16.3 1.88 16.3 1.92 -4.3 6.26 -4.1 6.21 Figure 3. MAX2653 GPS performance, input return loss (S11) for high-gain (active trace) and low-gain (memory trace). Figure 4. MAX2653 GPS performance, forward gain (S21) for high-gain (active trace) and low-gain (memory trace). Figure 5. MAX2653 GPS performance, reverse isolation (S12) for high-gain (active trace) and low-gain (memory trace). Figure 6. MAX2653 GPS performance, output return loss (S22) for high-gain (active trace) and low-gain (memory trace). Also See: Product Line Page Technical Support Page Wireless, RF, and Cable ICs MAX2653 Related Parts   APP 3248: Jun 25, 2004 MAX2653 GSM900 and DCS1800/PCS1900 Dual-Band, Low-Noise Amplifiers Full Data Sheet (PDF, 320kB) Automatic Updates Would you like to be automatically notified when new application notes are published in your areas of interest? Sign up for EE-Mail™. We Want Your Feedback!   Download, PDF Format (246kB)  AN3248, AN 3248, APP3248, Appnote3248, Appnote 3248