By Gibin Bose, Design Engineer at Farran Technology RF power amplifiers (PA) is a type of electronic amplifier that is used to increase the power level of radio frequency signals. In a typical radio transmitter (see Figure 1), RF power amplifier is present at the final stage, its output driving the antenna, and is responsible for the crucial task of amplifying the RF signal to the required power level for free space transmission. Radio transmitters are used in transmitting information over a distance in several applications including satellites, mobile communication, collision avoidance, Internet of Things (IoT), weather forecast, radars and so on. The increasing demand to transmit more information in a limited bandwidth coupled with the requirement of high efficiency of transmitters pose a serious challenge to RF engineers. Modern communication systems mostly use signals containing both amplitude and phase modulation and linear amplification is a necessity in these systems to avoid distortion and adjacent channel interference. Power amplifiers with high saturated output power (Psat), efficiency and good linearity play a critical role in the design of radio transmitters with high efficiency, longer physical range and good linearity. RF power amplifiers are implemented using transistors that operate in the linear region and based on how much of the cycle of the sinusoidal radio signal the given transistor is conducting, they can be classified into different classes (A, B, AB, C, D, F, G, I). Additionally, in the recent years to meet the increasing demands of higher output power, efficiency, and linearity, amplifier designers are utilizing various techniques including envelope tracking, digital predistortion, load modulation and dynamic biasing. Move towards GaN technology over silicon in transistors is also serving the purpose of higher power density, efficiency, higher temperature tolerance, reduction in size and wider bandwidth capabilities. Critical Figures of Merit Saturated output power, efficiency, linearity, gain, bandwidth, return loss and heat dissipation are some of the critical parameters of an RF power amplifier. Saturated Output Power (Psat): Saturated output power of an amplifier is the maximum output power amplifier can provide under the fixed recommended operating considerations of the amplifier. Efficiency: Efficiency of a power amplifier is commonly expressed either using power added efficiency () or drain efficiency. Power added efficiency is the ratio of added RF power to DC supply power expressed in percentage, Drain efficiency is the ratio of output RF power to DC supply power expressed in percentage, Higher saturated output power and efficiency of an amplifier plays a key role in extending the maximum range of transmitters and limiting the power consumption requirements of systems where these amplifiers are used. Gain: The primary function of an amplifier is to increase the amplitude of the signal at its input and this increase in the signal amplitude is quantified by gain. Gain, usually measured as small signal gain is the ratio of the output power to input power expressed in dB in the linear region of operation and under fixed recommended operating conditions for the amplifier. Return Loss: Return Loss () of an amplifier is the measure of the ratio of the incident to reflected power at either port expressed in dB. where Pi is the incident power and is the reflected power. Linearity: An amplifier provides a constant gain until a specific input power level and then there would be drop in gain resulting in compression effect i.e. the amplifier output power starts to saturate. The one dB compression point (P1dB) is the power level (input/output) where the gain is 1dB lower than the small signal gain. Beyond the P1dB point, amplifier becomes a non-linear device and can produce distortion, harmonics and intermodulation products. Farran offers a broad range of standard and custom-built power amplifiers over the frequency range of 18 GHz – 250 GHz. Access our website for more details and to contact us
By Gibin Bose, Design Engineer at Farran Technology
RF power amplifiers (PA) is a type of electronic amplifier that is used to increase the power level of radio frequency signals. In a typical radio transmitter (see Figure 1), RF power amplifier is present at the final stage, its output driving the antenna, and is responsible for the crucial task of amplifying the RF signal to the required power level for free space transmission.
Figure 1. A conceptual diagram of Tx Module
Radio transmitters are used in transmitting information over a distance in several applications including satellites, mobile communication, collision avoidance, Internet of Things (IoT), weather forecast, radars and so on. The increasing demand to transmit more information in a limited bandwidth coupled with the requirement of high efficiency of transmitters pose a serious challenge to RF engineers. Modern communication systems mostly use signals containing both amplitude and phase modulation and linear amplification is a necessity in these systems to avoid distortion and adjacent channel interference. Power amplifiers with high saturated output power (Psat), efficiency and good linearity play a critical role in the design of radio transmitters with high efficiency, longer physical range and good linearity.
RF power amplifiers are implemented using transistors that operate in the linear region and based on how much of the cycle of the sinusoidal radio signal the given transistor is conducting, they can be classified into different classes (A, B, AB, C, D, F, G, I). Additionally, in the recent years to meet the increasing demands of higher output power, efficiency, and linearity, amplifier designers are utilizing various techniques including envelope tracking, digital predistortion, load modulation and dynamic biasing. Move towards GaN technology over silicon in transistors is also serving the purpose of higher power density, efficiency, higher temperature tolerance, reduction in size and wider bandwidth capabilities.
Critical Figures of Merit
Saturated output power, efficiency, linearity, gain, bandwidth, return loss and heat dissipation are some of the critical parameters of an RF power amplifier.
Saturated Output Power (Psat): Saturated output power of an amplifier is the maximum output power amplifier can provide under the fixed recommended operating considerations of the amplifier.
Efficiency: Efficiency of a power amplifier is commonly expressed either using power added efficiency () or drain efficiency. Power added efficiency is the ratio of added RF power to DC supply power expressed in percentage,
Drain efficiency is the ratio of output RF power to DC supply power expressed in percentage,
Higher saturated output power and efficiency of an amplifier plays a key role in extending the maximum range of transmitters and limiting the power consumption requirements of systems where these amplifiers are used.
Gain: The primary function of an amplifier is to increase the amplitude of the signal at its input and this increase in the signal amplitude is quantified by gain. Gain, usually measured as small signal gain is the ratio of the output power to input power expressed in dB in the linear region of operation and under fixed recommended operating conditions for the amplifier.
Return Loss: Return Loss () of an amplifier is the measure of the ratio of the incident to reflected power at either port expressed in dB.
where Pi is the incident power and is the reflected power.
Linearity: An amplifier provides a constant gain until a specific input power level and then there would be drop in gain resulting in compression effect i.e. the amplifier output power starts to saturate. The one dB compression point (P1dB) is the power level (input/output) where the gain is 1dB lower than the small signal gain. Beyond the P1dB point, amplifier becomes a non-linear device and can produce distortion, harmonics and intermodulation products.
Farran offers a broad range of standard and custom-built power amplifiers over the frequency range of 18 GHz – 250 GHz.
