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Abridged Glossary of Amplifier Terminology
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Frequency Range
Gain
Gain Flatness
Noise Figure
Saturated Output Power
RF Burnout
Output Power at 1 dB Compression Point
Voltage Standing Wave Ratio (VSWR)
Reverse Isolation
Intercept Point for Intermodulation Products
Dynamic Range (DR)
Spurious-Free Dynamic Range (DRS)
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Amplifier Products
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Series UVLN, Low Noise RF and Microwave Amplifiers
Series UVOPA Power Amplifiers
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Frequency Range
The amplifier band which meets all its electrical specifications e.g., gain, noise figure, power output, intermodulation products, and VSWR.
Gain
The minimum gain across a specified frequency range. This is the small signal gain typically measured 20 dB below the 1 dB compression point.
Gain Flatness
The maximum difference between the minimum and maximum small signal gain across the band at any constant temperature.
Noise Figure
Direct measure of the noise added by the amplifier to the input white thermal noise presented at the output. The amplifier input white thermal noise plus the amplifier noise figure comprise the total
noise power level at the output of the amplifier. This level sets a lower limit on the dynamic range of the amplifier, specifically the power level at which a signal can be detected above the noise.
A 1 dB improvement in noise figure thus corresponds to a 1 dB improvement in the minimum detectable signal and in the dynamic range of the amplifier.
Saturated Output Power
Fig 33
The maximum output ower hat an mplifier can generate. This power level is usually constant for input drive levels ranging from a sufficient level to cause hard gain compression to a maximum input power, if specified.
This parameter is typically a specified performance characteristic where maximum output power levels are essential and system linearity is less
important.
RF Burnout
Device failure due to excessive RF overdrive. 20 to 100 mW is enough power to cause burnout in low noise amplifiers. For increased power handling capability, amplifiers may be supplied with RF limiters. This feature can add approximately 0.5 to 1 dB to the amplifier noise figure due to limiter insertion loss.
Output Power at 1 dB Compression Point
Output power generated by the amplifier when driven by an input level sufficient to cause a gain compression of 1 dB from the amplifier's small signal value. The output power level at 1 dB gain compression is typically 3 dB below the saturated output power level. This performance characteristic is generally specified when system linearity or wide dynamic range is most important.
Voltage Standing Wave Ratio (VSWR)
A measure of the ratio between the power reflected from one port of the amplifier and the power incident upon it. Output VSWR is basically a measure of how much power is reflected back from the amplifier output port when an external signal is applied to that port.
Reverse Isolation
Reverse isolation defines the isolation between the input and output of an amplifier. It is tested by injecting a signal into the output port and measuring its level at the input.
Intercept Point for Intermodulation Products
A non-linear phenomenon, such as intermodulation products can be defined as the difference in dBs between the levels of the fundamental and the level of the spurious signals. These spurious signals can be observed with respect to the input signal by means of a theoretical tool, the Intercept Point.
This point is where the linear extension of a particular “distortion” intersects the linear extension of the input vs output line. The intermodulation product characteristics can be calculated from the intermodulation equation below. These characteristics can also be obtained either by using the intercept diagram (see Figure 34) or by direct measurement.
Amplifiers are usually characterized by their 2nd and 3rd order
intercept points. The 2nd and 3rd order intercept points are the points where the transfer curves of the 2nd and 3rd order intermodulation products intersect the fundamental signal curve. The slope of the fundamental signals is 1:1 while the slope of the 2nd and 3rd order products are 2:1 and 3:1, respectively. Therefore, the 2nd order products are as far down from the fundamental as the fundamental is from the intercept
point and the 3rd order products are twice as far down. The relationship between the intermodulation products and the intercept points is explained by the following equations:
IM2 = IP2 - POUT and IM3 = (IP3 - POUT)
IM2 and IM3 are 2nd and 3rd order intermodulation product,
respectively. IP2 and IP3 are 2nd and 3rd intercept points, respectively.
Pout is the output power of the fundamental signal.
In the small signal case, the level of the 3rd order intermodulation products for two equal input signals may be obtained from the intercept point. Graphically, the intercept point is obtained by linearly extending the desired signal past the compression point until it intersects the 3rd order point
(see Figure 34). The output power level of the intermodulation intercept point is typically 10 dB above the output power at the 1 dB gain compression point.
Figure 34
Dynamic Range (DR)
The dynamic range of an amplifier for a single input signal is defined as the difference between the input signal level that causes a 1 dB gain compression and the minimum detectable signal (MDS), which is defined as the noise level.
MDS = KT + 10 logBW +NF
Where: KT = -114 dBm; BW = Bandwidth in MHz; NF = Amplifier noise figure in dB Thus DR = Pin (at 1 dB) – MDS. Fundamental Signal Input Power Figure 34. Intercept Diagram Output Power (dBm)
Spurious-Free Dynamic Range (DRS)
Where more than one signal is involved, a spurious-free dynamic range (DR) is defined as the difference between the input signal level of the intermodulation products and the minimum detectable signal (MDS).
DR2 = 1/2 (IP2 −G − MDS) and DR3 = 2/3(IP3 −G − MDS)
where
DR2 and DR3 are the Dynamic Range related to the 2nd order and 3rd order distortion, respectively; G is the amplifier gain.
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