Wideband Low Noise Amplifier

This application note discusses the use of Avago Technologies' MGA-675T6 for 5-6 GHz applications. The MGA-675T6 is internally integrated with shutdown and biasing circuitry, which simplifies the external circuitry. The shutdown feature allows the low noise amplifier (LNA) to be easily deactivated using an external voltage control, making it suitable for mobile receivers where the amplifier can be turned off to reduce current consumption and extend battery life. Utilizing Avago Technologies' proprietary 0.5-micron GaAs E-pHEMT technology (Enhancement-mode pseudomorphic high electron mobility transistor), the MGA-675T6 provides excellent linearity, high gain, and a very low noise figure at low voltage and current. These characteristics are critical for enhancing receiver sensitivity. The low operating voltage and current are essential for modern portable devices, such as notebooks or mobile devices equipped with multiple wireless standards (WiMAX, WLAN, GPS, and Digital Television). The simultaneous use of these functions often leads to high power consumption, particularly for digital TV, which requires significant power for image display. Therefore, power efficiency is crucial for extending battery life in portable devices. When operating at 3 V and 10 mA, the MGA-675T6 demonstrates performance at 5.5 GHz on the demonstration board with typical values of 1.75 dB noise figure, over 17 dB gain, -3 dBm IIP3, and -9 dBm IP1dB. The device can be easily shut down via an external control voltage, drawing almost zero current in this state. The MGA-675T6 is packaged in an Ultra-thin Small Leadless Package (UTSLP) with a low profile of 0.4 mm and a compact footprint of 2.0 mm x 1.3 mm, requiring minimal space on a printed circuit board. The simplified internal circuitry and pin configuration of the MGA-675T6 are illustrated in Figure 1. The integrated bias circuitry simplifies external biasing application circuits. Unlike typical depletion-mode pHEMTs, the enhancement-mode pHEMT LNA in the MGA-675T6 requires only a positive voltage supply for biasing. In this design, Vdd (pin 6), RF_OUT (pin 5), and Vshutdown (pin 1) are supplied with +3 V. The device draws approximately 10 mA with a +3 V supply voltage in amplifier mode, while the current drawn at the Vshutdown pin is less than 0.3 mA. In shutdown mode, the Vdd and Vshutdown pins draw almost zero current. Mobile devices often have limited battery life, necessitating high power efficiency. The shutdown feature allows the amplifier to be turned off when not in use, significantly improving power efficiency. The MGA-675T6 includes an integrated shutdown circuit that can be easily activated by leaving the Vshutdown pin open or applying 0 to 0.2 V to it while maintaining Vdd at +3 V. Figure 3 presents the gain versus shutdown voltage plot at various Vdd voltages, indicating that the current drawn by both the Vdd and Vshutdown pins in shutdown mode is nearly zero. Figure 4 illustrates the application circuit of the MGA-675T6 for 5-6 GHz. The input matching of the device is achieved through a microstrip short-stub followed by a series capacitor (C1), optimizing the low noise figure and high gain across a wide frequency range of 5 to 6 GHz. The input shunt short-stub (TL1) also enhances the electrostatic discharge (ESD) protection at the RFin pin (pin 2).

The MGA-675T6 is designed to operate effectively within the specified frequency range of 5-6 GHz, making it suitable for various applications, including mobile communication and wireless data transmission. The device's low noise figure is essential for maintaining signal integrity, particularly in sensitive applications where signal quality is paramount. The integrated biasing and shutdown features not only reduce the complexity of the overall design but also contribute to the efficient power management of devices that rely on battery operation. This is particularly relevant in scenarios where multiple wireless technologies are employed simultaneously, as is common in modern mobile devices. The ability to switch off the amplifier when not in use allows for significant power savings, extending battery life and enhancing user experience. The compact size of the UTSLP package allows for easy integration into space-constrained designs, making the MGA-675T6 an attractive option for engineers looking to optimize performance while minimizing board real estate.This application note discusses the application of Avago Technologies` MGA-675T6 for 5-6 GHz application. The MGA-675T6 is integrated internally with shutdown and biasing circuitry. Besides reducing the complexity of the external circuitry, the shutdown circuitry allows the LNA to be easily shut down by an external voltage control.

This feature ma kes the MGA-675T6 suitable to be used in a mobile receiver where the amplifier can be switched off easily to reduce current consumption and to extend a battery life. By using Avago Technologies` proprietary 0. 5-micron GaAs E-pHEMT technology (Enhancement-mode pseudomorphic high electron mobility transistor), the MGA-675T6 can achieve excellent linearity, high gain and very low noise fi gure at low voltage and current.

These are the key parameters to improve the sensitivity of the receiver. The low operating voltage and current is essential to modern portable devices such as notebook or mobile devices that are equipped with multiple wireless standards (WiMAX, WLAN, GPS, and Digital Television etc. ). Simultaneous applications of these functions always require high power consumption, especially digital TV which heavily involves image display.

Thus, great power effi ciency to extend battery life becomes an important requirement for portable devices. While operating at 3 V and 10 mA, the MGA-675T6`s measured performance at 5. 5 GHz on the demonstration board is typically: 1. 75 dB NF, >17 dB gain, -3 dBm IIP3, and -9 dBm IP1dB. The device can be easily shut down through an external control voltage, and it will draw almost zero current ( ­A range).

The MGA-675T6 is housed in an UTSLP (Ultra-thin Small Leadless Package) package with a very low profi le (0. 4 mm) and small footprint (2. 0 G— 1. 3 mm2) that requires only a small area of printed circuit board. Figure 1 shows the simplifi ed internal circuitry and pin confi guration of the MGA-675T6. The integrated bias circuitry inside the MGA-675T6 simplifies the external biasing application circuit.

Unlike a typical depletion-mode pHEMT, the enhancement-mode pHEMT LNA in the MGA-675T6 only requires a positive voltage supply to bias the LNA. In this design, Vdd (pin 6), RF_OUT (pin 5) and Vshutdown (pin 1) are supplied with +3 V. The device draws approximately 10 mA with a +3 V supply voltage in the amplifi er mode, and the current drawn at the Vshutdown pin is <0.

3 mA. When the device is operating in the shutdown mode, the Vdd and Vshutdown pins draw almost zero current ( ­A range). Mobile devices always have limited battery life and thus require great power efficiency. A shutdown feature allows the amplifier to be turned off while not in use, and this will greatly improve the power efficiency.

The MGA-675T6 features an integrated shutdown circuit. It can be easily shut down by leaving the Vshutdown pin open or applying 0 to 0. 2 V to it while maintaining the Vdd at +3 V. Figure 3 shows the gain versus shutdown voltage plot at various Vdd voltages. The current drawn by both the Vdd and Vshutdown pins in the shutdown mode is almost zero. Figure 4 shows the application circuit of the MGA-675T6 for 5-6 GHz. The input matching of the device is formed by a microstrip short-stub followed by a series capacitor, C1, to give a low noise fi gure and high gain over a very wide frequency range of 5 to 6 GHz. The input shunt short-stub (TL1) also helps to improve the ESD level at the RFin pin (pin 2). 🔗 External reference