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MAX2685 Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX2685 Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 10 page Detailed Description The MAX2685 consists of five major components: a low-noise amplifier (LNA), an LNA bypass switch, a downconverter mixer, a local-oscillator (LO) buffer, and a power-management block. Low-Noise Amplifier (LNA) The LNA is a wideband, single-ended cascode amplifi- er that operates over a wide range of frequencies. The input of the LNA (LNAIN) requires an appropriate matching network and a DC-blocking capacitor. The typical operating circuit shown in Figure 1 is optimized for frequencies around 880MHz, requiring only a 0.1µF capacitor in series with a 12nH inductor. See Table 1 for the LNA “S” parameters for matching to other fre- quencies. The output of the LNA (LNAOUT) is internally biased to VCC. It is internally matched to 50 Ω and incorporates an internal DC-blocking capacitor. LNA Bypass Switch and Gain Control When a large input signal is present, enable the LNA bypass function to increase linearity and reduce supply current. Set GAIN low to enable the LNA bypass func- tion. Receive Mixer The downconverter mixer is a wideband, single-bal- anced design with a low noise figure and high linearity. The RF signal at the MIXIN port is mixed with the signal at the LO port, and is downconverted to an IF frequen- cy at the differential IF port. RF Input The MIXIN input requires a simple external matching network and a series DC-blocking capacitor. See Figure 1 for a matching network example, optimized for 880MHz operation. Table 2 lists mixer “S” parameters for matching to other frequencies. Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer _______________________________________________________________________________________ 7 Table 1. LNA Typical S-Parameters (VCC = +3V, TA = +25°C) |S11| MAG FREQUENCY (MHz) 800 0.761 S11 PHASE (degrees) -64.5 |S21| MAG S21 PHASE (degrees) 177.9 4.98 |S12| MAG S12 PHASE (degrees) -163.7 |S22| MAG S22 PHASE (degrees) -107.3 0.376 0.018 -68.6 167.2 5.06 -167.1 840 0.753 -107.0 0.264 0.022 -73.2 156.6 5.07 -171.3 880 0.747 -94.6 0.172 0.026 -78.0 146.6 4.91 -175.7 920 0.733 -62.9 0.149 0.030 -82.8 137.7 4.68 178.0 960 0.719 -42.4 0.200 0.035 -87.5 130.3 4.40 171.0 1000 0.693 -38.8 0.263 0.039 -45.6 73.0 0.188 71.9 800 0.625 -91.3 0.483 0.191 -48.1 65.5 0.195 64.2 840 0.621 -91.3 0.423 0.198 -50.9 58.1 0.199 56.7 880 0.619 -89.9 0.370 0.201 -53.3 51.6 0.200 50.3 920 0.611 -86.1 0.337 0.202 -55.5 46.1 0.200 44.7 960 0.608 -80.9 0.322 0.201 -57.5 41.2 0.200 40.0 1000 0.607 -76.7 0.317 0.200 High-Gain Mode (GAIN = VCC) Low-Gain Mode (GAIN = GND) |
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Similar Description - MAX2685 |
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