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MAX2180 LNA based on the AM / FM active antenna LNA design

In Electronic Infomation Category: M | on April 13,2011

This application note describes

AM / FM car antenna, a reference design (RD). Designed with active antenna modules for highly integrated AM / FM low noise amplifier (LNA) MAX2180. LNA in the AM and EL4585CS datasheet and FM signals are integrated on the Maxim channel automatic gain control technology, with user-selectable set point. AM and EL4585CS price and FM signal pathway can also change the maximum gain to meet the various needs of users. RD shows a detailed integrated automotive solutions to the flexibility and EL4585CS suppliers and performance.


Car antenna requires a smaller, more integrated solutions, while ensuring modern AM / FM performance required for wireless communication devices. Some solutions require automatic gain control (AGC), and some fixed-gain LNA, in order to obtain the lowest cost. Some solutions for the active antenna to provide a power supply voltage, but most still use the battery power supply. The antenna solutions provider for the challenge is: how to avoid the need for repeated design of the discrete solutions or do not use expensive IC (still need an external PIN diode and regulator) the circumstances to meet a wide range of industry requirements. Resources and limited space, the antenna solutions provider is necessarily the ideal high-performance, low cost and highly flexible IC, and the need to re-design, BOM changes and changes in circuit board, you can easily meet various requirements.

Few manufacturers now provide integrated active antenna for the AM / FM solutions. Unfortunately, they need to provide an external PIN diode AGC. These solutions in the use of battery power, you also need a power supply, or an external regulator. Increase in the cost of external components to expand the solution footprint. If you do not need AGC, solutions, discrete devices commonly used to obtain the lowest cost. Discrete design problem, gain, power supply voltage or any change in footprint will lead to re-design, which takes more design resources, design resources are very scarce in most cases.

Optimal antenna solutions and MAX2180

Maxim Integrated Products has developed a AM / FM antenna solution, which integrates all the active components, car antennas to meet the demanding needs of today. Antenna using MAX2180 LNA. MAX2180 uses an internal high-voltage CMOS technology, in a small 4mm x 4mm TQFP package integrates the AM and FM AGC, and the pressure regulator. This design avoids all the PIN diode and an external regulator circuit or transistor, but can also work with batteries or power supply. MAX2180 can achieve maximum AM and FM gain, and AGC set point variable. It also includes the antenna monitoring functionality, the inhalation of 15mA current under fault conditions.

LNA chip voltage regulator circuit in the 7V to 24V. To prevent overheating damage to the integrated temperature sensor through the foldback current limit the maximum junction temperature. This ensures that the amplifier in any environment, working conditions are maintained.

AM input is high impedance, low-impedance output, FM amplifier provides input and output impedance of 50. AM gain the maximum by changing the external resistor to set the range 0dB to 6dB. FM gain in 5.8dB maximum to 8.5dB (R1 = 0) range. To improve the noise figure, R1 should be 390, which will increase to 10.0dB gain range to 10.8dB. Two signal paths are used Maxims patented AGC circuit gain control range of 30dB. In addition, AGC set point variable, for the host to provide the desired maximum output level.

Design using MAX2180, the use of data in the table to select the desired signal path gain and AGC set point, simplifies the design. This custom made range of parameter values ??to meet the various needs of a design without having to re-layout of the circuit board. Shown in Figure 1, compared with competing solutions, MAX2180 provides a higher level of integration, but also has the flexibility to meet various needs. Figure 2 shows the application of single-antenna solutions schematic.

Figure 1. MAX2180 highly integrated solutions (A) and AM / FM antenna active competition program (B) Comparison

Figure 2. Using a single antenna solution MAX2180 application schematic

Design Example

Our test case for small cars to a low-gain antenna. Such applications require a larger gain, but small cars in the short cable to the host reduces the loss from the antenna, the target for the maximum input levels on the AM for the + 80dBuV, FM to +95 dBuV.

AM: pin 1 resistance = 0, a gain of 6.5dB (Table 1); pin 2 shorted to ground, AM output AGC set point +79 dBuV (Table 2).

FM: pin 10 shorted to ground, FM gain of 8.5dB (Table 3); pin 12 on the ground resistance = 39k, FM output AGC protection point of +94 dBuV (Table 4).

Table 1. AM signal path gain

pin 1 ()

AM gain (dB , a typical value )

0 < / SPAN>

6.5 < / SPAN>

22 < / SPAN>

5 < / SPAN>

68 < / SPAN>

2.5 < / SPAN>

180 < / SPAN>

0.5 < / SPAN>

330 < / SPAN>


Table 2. AM signal path set point

pin 2

AM output set point (dBV , a typical value )

Ground < / SPAN>

79 < / SPAN>

Open < / SPAN>

83 < / SPAN>


86 < / SPAN>

Table 3. FM signal path gain

pin 10

FM gain (dB , typ; no external resistor )

FM gain (dB , typ; external resistor = 390) < / TD>


8.5 < / SPAN>

10.8 < / SPAN>

Open < / SPAN>

7.1 < / SPAN>

10.3 < / SPAN>

Ground < / SPAN>

5.8 < / SPAN>

10 < / SPAN>

Table 4. FM signal path set point

pin 12 (k)

FM output protection point (dBV , a typical value )

0 < / SPAN>

104 < / SPAN>

10 < / SPAN>

100 < / SPAN>

18 < / SPAN>

96 < / SPAN>

27 < / SPAN>

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