4/4/2024 0 Comments Dbfs decibels full scaleThis is understandable because there is no universally accepted technical definition. Understanding dynamic range is complicated by the fact that different vendors describe and measure it differently. Maximizing dynamic range is paramount in instrumentation design, so that both small and the large signals are measured accurately. This noise is inherent in the electronics associated with transducer elements and transducer signal conditionings. If the dynamic range is too low, large signals will typically be clipped and distorted, while small signals are buried in system noise. This document describes the concept of dynamic range, the different methods used to assess it, and how Crystal Instruments assesses dynamic range of the instruments.ĭynamic range is one of the critical performance specifications of a dynamic measurement system. This capability makes setup and testing more simplified in comparison with an instrument capable of only a lower dynamic range. Both full scale 10 volt signals and very small microvolt signals are measured at the same time with no adjustments. The main advantage of this high dynamic range is that it eliminates the need to adjust the input gain/range settings on the front end, thus simplifying the setup and measurement process. This kind of performance has never before been achieved with such small, portable, and low cost devices. One of the breakthrough features of the CoCo-80, Spider-80X, and Spider-81 is their outstanding dynamic range performance of 160 dBFS. Where P dBm is the signal generator power in dBm, V rms is the rms voltage, R is the system impedance (50 Ω in this case), P 0 is 1 mW.Define and Measure Dynamic Range Download PDF | © Copyright Crystal Instruments 2018, All Rights Reserved. Where V rms is the rms voltage, and V p-p is Peak-to-Peak voltage Where V IN is the input voltage, and V FS is the full-scale voltage So, you can safely say “my front end ate all the dBs”. Now that there are other components (wideband balun, matching network, kickback control, etc.) they all contribute to insertion loss which results in an attenuated signal at -6.7 dBFS. Looping back to our question once more, the premise that a 7.6 dBm signal would be needed to get a -1 dBFS signal at the ADC is correct, if there is nothing besides the signal generator in front of the ADC. Front-end network with band-pass filter and signal generator. So, revisiting Figure 1 again, this time with some annotations, we arrive at Figure 2.įigure 2. Note that this is not including the insertion loss through a band-pass filter or connector cables. Therefore, the signal generator has to provide a signal that corresponds to about 3.03 V p-p or roughly 14 dBm. This results in a single-ended input of about 3.03 V p-p. The balun termination has a 6 dB loss across it, so the swing on each leg of the balun should be roughly twice the 1.515 V. Since the loss across the 10 Ω resistor is pretty small, we can assume that this is the voltage out of the termination network. For a default full scale level of 1.7 V p-p, a –1 dBFS signal would be 1.515 V p-p. A reference impedance of 50 Ω is used for the math. So let us work our way outward of the ADC to see how much power out of the signal generator is needed to get a –1 dBFS signal at the ADC. ![]() This resistor helps in improving third harmonic performance by reducing the kickback coming from the ADC's sample and hold stage. There is a small amount of insertion loss presented by the series resistance in front of the ADC (R kB). This matching network is required to provide a wideband match to the balun output. The matching network which follows the balun (R s and R SH) adds another 6 dB. A quick look at the data sheet for the BAL-0006SMG indicates that it has a 6 dB insertion loss across it. The single-ended-to-differential conversion is done by a wideband balun, the BAL-0006SMG. Default front-end network for the AD9680 evaluation board. Let us take a closer look at the default front-end network for the AD9680 ADC.įigure 1. However, when you do that, the ADC's single tone FFT output shows –6.7 dBFS. In order to achieve –1 dBFS on a 1.7 V p-p full scale ADC, one would only require 7.6 dBm signal level (based on a reference impedance of 50 Ω). Benchtop RF signal generators usually output signals in dBm. Whether it is 1 dB or 0.5 dB below full scale, it is done so as to prevent clipping of the signal if one were to run the ADC inputs at full-scale (0 dBFS). Some data sheets specify the distortion at 0.5 dB below full scale. Quite often, the ADC (analog-to-digital converter) performance is specified at –1 dBFS. However, I am seeing –15 dBFS! Who ate all of my dBs? Answer: I am setting my signal generator to output a CW tone at a certain power, which per my math, should give a –1 dBFS signal at the ADC.
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