What is a Detector Log Video Amplifier (DLVA)?

A Detector Logarithmic Video Amplifier (DLVA) consists of a detector followed by a logarithmic video amplifier (LVA). The detector converts the RF energy into a DC voltage which is then amplified by an amplifier with a logarithmic transfer function. A DLVA converts an RF signal with a large dynamic range into a video signal/voltage with a smaller dynamic range. The output voltages can then be displayed on a screen.

The basic configuration of a DLVA is a detector (Schottky barrier diode or a zero bias tunnel diode) followed by a logarithmic video amplifier (LVA). The detector detects the pulse or CW signal and produces a video signal (i.e Voltage), which is fed into the LVA and amplified logarithmically. The LVA transforms the scale of the video signal from a linear scale to a logarithmic scale in order to observe the RF signals with a wide amplitude range. DLVA is ideal for applications such as phased array radar receivers, passive direction finding receivers (such as radar warning receivers) and channelized receivers.

To better visualize this, think of a radar screen, where the distance of a target is calculated based on the reflected power received by a radar receiver. Let's assume that the receiver gets the following power levels at different points of time:

The higher the power level, the closer the target to the receiver. When showing these power levels on a screen, we are not able to easily differentiate 0.001 W, 0.005 and 0.01 W from each other on a linear scale - as the scale is divided in to equal values from 0.001 to 100 W. However, if you look at the same values on a Logarithmic scale, it is quite easy to differentiate them. This is why we use DLVA's. The DLVA detects an input signal, then amplifies it and represents it on a log scale which makes it much easier to read.

Click here to search for Detector Logarithmic Video Amplifiers (DLVAs) from the leading manufacturers.

Dynamic range is a key parameter for many types of test and measurement equipment, analog-to-digital converters (A/Ds), digital-to-analog converters (D/As), radar receivers, and receivers in general. In some applications, a greater effective dynamic range than what the receiver hardware is capable of is required. Hence, devices, such as detector log video amplifiers (DLVA), which performs a logarithmic transfer function that compresses the dynamic range of a signal without down converting the signal. As the logarithmic transfer function of a DLVA is known, calculating the real signal strengths are relatively straightforward. After an RF signal is passed through a DLVA, the output signal is known as the video signal.

DLVAs are often used in radar receivers, such as phased array radar, passive direction finding radar, and channelized radar used to secure the airspace around airbases and detect unauthorized intrusions. Types of DLVAs are also used in common RF test and measurement equipment to enhance their dynamic range performance while maintaining high linearity and sensitivity. The fast response time and broadband capability of some DLVAs make them ideal for electronic warfare (EW), signal intelligence (SIGINT), instantaneous frequency measurement (IFM) receivers, and other applications that require a fast response and relatively flat frequency response compared to other RF detectors.

Several types of DLVAs exist, including successive DLVAs (SDLVAs) and broadband DLVAs. SDLVAs used a different circuit typology than DLVAs, and don’t require a detector. Instead, SDLVAs use successive gain compression to emulate the logarithmic transfer function of a DLVA. In order to enhance the broadband performance of a DLVA, a combination of a hybrid combination of DLVAs and SDLVAs can be used to make a much broader bandwidth device with multi-octave frequency performance. Broadband log video amplifiers are particularly useful in ultrawide bandwidth agile radar systems and test and measurement equipment that spans several frequency octaves.