Wideband Amplifiers – Variable and Temperature-Compensated Gain

Many types of RF systems and applications that span from the upper end of microwave frequencies to the lower end of mmWave have arisen in recent years. Meeting system requirements over such a wide bandwidth and high frequency range, or even a broad sub-band requires that system performance parameters be stable, and the parameter that most often concerns microwave/mmWave system designers is gain. Mini-Circuits addresses these concerns with two amplifier types from our ZVA-series of wideband microwave/mmWave amplifiers that equip the system designer with either variable gain, or temperature-compensated, stable gain. Not only can gain be temperature-stable or variable, but at approximately 50 dB, it is also plentiful. Combine this with a low NF, high linearity and interactive telemetry, and Mini-Circuits’ wideband, variable and temperature-compensated gain amplifiers prove to be one of the highest-performing and most flexible amplifier solutions on the market today. Read on to find out how adjustable or temperature-stable gain and the ability to monitor output power can be beneficial when it comes to designing a system for any one of a number of applications.
Frequency, NF, Linearity and Gain Range
The wideband nature of the ZVA-VG(X) and ZVA-TC(X) amplifiers is shown in Table 1, where the bandwidth of the ZVA-18443VGX+ is greater than 25 GHz and the bandwidth of the ZVA-20543VGX+ and ZVA-20543TCX+ is 34 GHz. As mentioned at the outset, approximately 50 dB of gain is available from both solutions, with typical noise figures in the 4 to 5 dB range. High linearity may be an understatement, with all the amplifiers exhibiting a P1dB of +30 dBm (1W), and the 43.5 GHz amplifiers an OIP3 of +41 dBm (over 10W).

Table 1 also shows that the ZVA-18443VG(X)+ and ZVA-20543VG(X)+ have a gain adjustment range (also referred to as the attenuation range) of 17 dB. The gain can be adjusted digitally, utilizing a USB-to-TTL connection, as well as with a single, 3.3V full-scale, analog voltage. On the other hand, the ZVA-20543TC(X)+ has its gain internally temperature-compensated, and performs exceptionally well from -20⁰C to +60⁰C, as shown in Figure 1.

Should temperature compensation be required over a narrower temperature range or bandwidth, Mini-Circuits stands ready to accommodate our customers with solutions that will exhibit even better gain stabilization. In a subsequent section, our discussion will turn to the importance of having gain that is constant over temperature, or having the ability to adjust gain. For now, we turn our attention towards other important features of these wideband amplifiers.
Amplifier Protection, Monitoring and Control
Designing a robust amplifier requires built-in safeguards, and these wideband amplifiers from Mini-Circuits incorporate in-rush current limiting, and over-voltage and reverse voltage protection. Along with these protection features, the ZVA temperature-compensated and variable gain amplifiers furnish the internal temperature and detected RF output power, and trigger an alarm (temperature or current fault) to indicate a condition in excess of pre-set limits.
Mini-Circuits’ wideband ZVA-VG(X) and ZVA-TC(X) amplifiers can be turned on and off via an enable input (mute/unmute), and the ZVA-18443VG(X)+ and ZVA-20543VG(X)+ amplifiers can control gain over a 17 dB range either digitally, in 0.25 dB steps, or by utilizing a single analog voltage. These variable gain amplifiers, as well as the temperature-compensated amplifiers, can communicate with an interactive GUI via a TTL serial interface, the most straightforward way being a USB-to-TTL connection.
Microwave and mmWave Amplifier Applications – Automatic Gain Control
Applications for amplifiers in the 18 to 54 GHz frequency range are numerous. These include radar, SATCOM (block upconverters, for instance), electronic warfare, communications, microwave radio, wireless 5G FR2 infrastructure, high capacity backhaul, and test instrumentation (e.g 5G).
The variable gain feature of the ZVA-18443VG(X)+ and ZVA-20543VG(X)+ amplifiers is useful in system design to balance and fine-tune system performance without the need to repeat cascade analyses. Gain can be continuously adjusted for changes in signal levels to maximize the dynamic range of a system. Additionally, gain can be adjusted for variations in reference temperature. When using a lookup table with gain entries for several discrete reference temperatures, linear interpolation can be performed to adjust the gain in closed-loop fashion as system temperature varies. The reference temperature may be the internal temperature monitor of the amplifier itself, or some other reference temperature in the system. This practice is commonplace in RF system design. For wideband amplifiers, the lookup table is often three-dimensional, including frequency in addition to temperature and gain as entries.
Certain systems require a wideband amplifier with constant gain over temperature, and that is where the ZVA-20543TC(X)+ finds utility. In the center of the band, from -20⁰C to +60⁰C, the ZVA-20543TC(X)+ gain varies by little more than 1 dB peak-to-peak! Uncompensated amplifiers often vary by 5 to 6 dB peak-to-peak.
Automatic Level Control
Another common application for the ZVA-18443VG(X)+ and ZVA-20543VG(X)+ variable gain amplifiers is to utilize the output power detector and gain control to design an automatic level control (ALC) system, wherein the output power level is held constant while the input level and temperature vary. Signal generators commonly employ ALC to stabilize their RF output power. RF receivers may utilize ALC to optimize dynamic range in the IF or baseband section. RF power amplifiers that are required to output precise power levels turn to ALC as a means of control. Additionally, ALC is often used in RF power amplifiers to transmit high crest factor signals without the associated signal distortion and spectral regrowth that comes with driving the amplifier into compression. Finally, ALC has long been utilized in RF power amplifiers as a means of protecting the amplifier from transmitting into high VSWR loads such as a broken antenna.
Mini-Circuits’ ZVA-TC(X) and ZVA-VG(X) – Temperature-Stable and Variable Gain Models
In this application note we described Mini-Circuits’ wideband amplifiers that have both variable gain (the ZVA-18443VG(X)+ and ZVA-20543VG(X)+) and temperature-compensated gain (the ZVA-20543TC(X)+). Our review included a table of specifications for these amplifiers as well as a figure showing temperature-compensated gain vs. frequency. Additionally, features that protect, monitor and control these amplifiers was introduced.
The market for amplifiers in the 18 to 54 GHz frequency range is vast, and a number of these markets were listed as applicable. Automatic gain control (AGC) was presented as a way to maximize the dynamic range of an RF system given widely varying input signal levels or to stabilize system specifications given changes in system temperature. The automatic level control (ALC) discussion emphasized the signal generator application, but also included ALC applications for receivers and RF power amplifiers.
The high-microwave-to-low-mmWave frequency range is increasing in popularity, coincident with the drive to build out 5G NR FR2 bands. Mini-Circuits continues to grow our ZVA line of amplifiers with temperature-compensation and variable gain to address a myriad of flexible solutions in this frequency range. Explore the ZVA wideband, temperature-compensated and variable gain amplifiers today.