Using the MAX2691 with an RF Input of 1090MHz

要約

Countries around the globe are implementing a more accurate way of tracking aircraft using the Automatic Dependent Surveillance-Broadcast (ADS-B) and eventually replacing radar as a primary surveillance method for Air Traffic Control (ATC). High performance, improved safety, reduced radio frequency (RF) pollution, cost-efficient are some of its notable features. The MAX2691 low-noise amplifier (LNA) can be a good fit for ADS-B application. The device achieves high gain, sub 1dB noise, and excellent linearity. This application note provides details on adapting it for use at 1090MHz.

Introduction

The MAX2691 LNA is designed for GPS L2 (1227.6MHz) applications. However, the MAX2691 LNA can also be tuned to 1090MHz by changing external matching components. This application note provides details for those external matching components and the performance of the tuned circuit.

Why Use the MAX2691?

Over time, communication standards change, and frequency spectrum is reallocated. However, many existing ICs can be adapted to evolve with these changes. The advantages include the following:

  • Time to production is reduced since you are using existing components requiring no supplier development time.
  • Cost is lower since currently mass-produced items are used.
  • Quality is improved since products are used that have a proven track record.
Table 1. Typical Performance at 1090 MHz for MAX2691 (Measured with an RF Input = 1090MHz, VCC= +2.85V)
BAND (1090MHz)
 
Noise Figure 0.92dB
Gain 17.53dB
RF Input Return Loss 13.80dB
RF Output Return Loss 12.20dB

RF input return loss data for MAX2691 tuned to 1090MHz

Figure 1. RF input return loss data for MAX2691 tuned to 1090MHz.

RF input return loss data for MAX2691 tuned to 1090MHz

Figure 2. Gain data for MAX2691 tuned to 1090MHz.

RF input return loss data for MAX2691 tuned to 1090MHz

Figure 3. RF output return loss data for MAX2691 tuned to 1090MHz.

RF input return loss data for MAX2691 tuned to 1090MHz

Figure 4. Application circuit for MAX2691 at 1090MHz.

Table 2. External Matching Components for Tuning MAX2691 to 1090MHz
Reference Designator On Board New Value
L1 8.2nH Inductor 12nH Inductor
C13 100pF Capacitor 8.2nH Inductor
C8 Open 2.2pF
CNEW* N/A 100pF
*Cut RF trace between RFOUT SMA and C8 and place 100pF
Table 3. Power Consumption
Power Calculations
 
Voltage (V) 2.85V
Current (I) 4.30mA
Power (P) 12.25mW