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MAX2531ETI Datasheet(PDF) 10 Page - Maxim Integrated Products |
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MAX2531ETI Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 27 page LNA linearity is required for cross-modulation suppres- sion. Use HGLL mode when the transmitter is off and cross-modulation is not a concern. The LNAs are designed to minimize input VSWR when changing modes. Use low-gain mode for receiving large signals and when high sensitivity is not required. The cellular band provides an additional gain mode (MG) for improved IP3 margin in CDMA medium-level interfer- ence condition. Downconverters The downconverters in these devices are double- balanced mixers. The cellular and PCS mixers have three gain modes: high linearity, low linearity, and low gain. The cellular and PCS mixers can route the IF sig- nal to either IF0 or IF1 port. IF_SEL = low routes the IF signal to IF0 port; IF_SEL = high routes the IF signal to IF1 port. The GPS mixer has only one mode, and it has a dedicated IF port (Table 2). All mixer inputs include on-chip matching networks to reduce the external com- ponent count. LO Generation Table 3 shows the options for the LO generation. The on-chip LO divider or multiplier allows triple-band oper- ation with a single VCO. The MAX2351 and MAX2531 have an LO multiplier that doubles the cellular band VCO for PCS band operation. Conversely, the MAX2358, MAX2537, and MAX2538 include an LO divider that divides the PCS VCO frequency down to cellular frequency band. The GPS LO is generated by a fractional frequency scaler, which enables a single VCO for operation in all three bands. The MAX2530 is designed for operation with a dual-band VCO. The PLL buffer output is provided for phase-locked loop operation. The PLL pin serves two functions: RF output signal for phase-locked loop operation and logic input to enable or disable this buffer. A logic high applied to this pin enables the PLL buffer; a logic low disables the buffer. A buffered LO output is provided to drive a transmit upconverter. It is controlled by the BUFFEN input. For time-division duplex applications, the buffer is available to drive the transmitter even when the rest of the chip is shut down. The port is internally AC-coupled, so a DC- blocking capacitor is not required. Bias Control The bias control input (BIAS pin) controls the IC bias current. Typically, connect a 20k Ω resistor to ground for normal operation. Smaller bias resistor values increase the supply current and linearity. Applications Information Cascaded LNA/Mixer Performance The LNA and mixer design optimizes cascaded perfor- mance in all gain and linearity modes. In high-gain/high- linearity mode, both the LNA and mixer have low noise figure, high gain, and high linearity. In this mode, the LNA has extra-high linearity for superior cross-modula- tion suppression. The high-gain/low-linearity mode is used when the transmitter is off and cross-modulation is not a concern. In the ultra-low-gain mode, the received signal is strong enough that sensitivity is not the limiting factor. This mode focuses on minimizing supply current. Tables 4, 5, 6 summarize the cascaded performance. LNAs The LNA inputs require external matching networks to optimize gain, linearity, noise figure, and return loss. A simple LC match is sufficient as shown in the Typical Application Circuit. The cellular and GPS LNA outputs are internally matched. The PCS LNA output requires an inductor pullup to VCC and a series capacitor as external matching elements. Table 7, 8, 9 show the S- parameters for each LNA. Tables 13, 14, 15 show LNA noise parameters. Mixers All mixer inputs are internally matched. The GPS and PCS mixer inputs require a DC-blocking capacitor; the cellular mixer does not. All IF outputs must be induc- tively pulled up to VCC. The inductive pullup may be used as part of the matching network. Because the dif- ferential IF output port is high impedance, a load resis- tor is typically used to ease the matching and establish the gain. A 3.3k Ω resistor is recommended for IF0 and IF1, and 8.2k Ω for the GIF port. The equivalent parallel RC impedance of the IF ports is typically 12.2k Ω in par- allel with 0.75pF. Tables 10, 11, 12 show S-parameters for the mixer input points. Quadruple-Mode PCS/Cellular/GPS LNA/Mixers 10 ______________________________________________________________________________________ ABBREVIATION MODE HGHL High gain/high linearity HGLL High gain/low linearity MG Midgain LG Low gain ULG Ultra-low gain HL High linearity LL Low linearity Table 1. Abbreviation for LNA and Mixer Modes |
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