Maxim公司MAX2742是CMOS單片GPS前端下變換器,器件的功耗非常低(2.4V時32mW),不需要昂貴的IF SAW濾波器或體積過大的IF基帶濾波器.MAX2742集成了低噪音放大器(LNA),混頻器,帶通濾波器(BPF),自動增益控制放大器(AGC),本地振蕩合成器,時鐘緩沖器和整數(shù)數(shù)字取樣器.本解決方案提供了完整的GPS前端解決方案.

Complete Stand-Alone GPS Receiver Solution with MAX2742
Abstract: A complete GPS solution is achieved with minimal external components, using the MAX2742 integrated CMOS RF front-end GPS receiver.

The MAX2742 is a CMOS, single-chip, GPS front-end downconverter. This state-of-the-art device consumes very low power (32mW at 2.4V), and eliminates the need for a costly IF SAW filter or bulky discrete IF bandpass filters. The MAX2742 integrates a low-noise amplifier (LNA), mixer, BPF, automatic-gain-control amplifier (AGC), local oscillator synthesizer, clock buffer, and internal digital sampler.
This device can interface with many commercially available GPS baseband ICs. It is suitable for many applications, including vehicle navigation, telematics, automatic security, asset tracking, location-based service (LBS), and consumer electronics. The external components required around the device are minimal for a complete GPS RF solution. The system block diagram can be found in the following section.

The MAX2742 works with an 18.414MHz* crystal or TXCO, and offers differential or single-ended** IF output at 1.023MHz. Total signal conversion gain is 120dB, with a noise figure of 4.5dB. The IF signal is sampled at the reference clock rate of 18.414MHz.

* Note: 18.414MHz is 18 times 1.023MHz, which is one-tenth of the GPS fundamental frequency 10.23MHz.

** Note: There are three IF output pins—one pair of differential outputs and one single-ended output. Selection is controlled by pin 10.

Complete GPS RF Front-End Solution

Figure 1 shows the important building blocks and features of Maxims complete GPS RF solution. Description of the building blocks can be found in Table 1; cascaded performances are shown in Table 2. Figure 2 shows the application circuit of the GPS receiver RF portion with the MAX2742.



Figure 1. GPS RF front-end block diagram.

Table 1. RF Portion System Building Block



Table 2. System Cascaded Performance





Figure 2. GPS RF portion schematic for MAX2742.

Complete Stand-Alone GPS Receiver Solution
There are more building blocks to construct a complete GPS receiver, other than just the RF plus baseband IC. As shown in Figure 3, an extra antenna supply-control block, a RESET circuit, and a delay circuit are needed. Description of the building blocks can be found in Table 3; cascaded performances are shown in Table 4.



Figure 3. Complete GPS receiver solution block diagram.

Table 3. System Building Block



Figure 4 shows the real PCB layout of the reference design. The complete solution only occupies 25mm x 25mm of PC board space.

Figure 4. GPS Receiver PCB layout.

Table 4. Module Performance (LNA + MAX2742 + SONY CXD2932)



Note 1: T.C. = test condition, N.M. = not measured

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