## Modern Amplifier Terms Defined
When Cp is 1, then 99.73% of the units pass specs and the process produces 0.27%. rejects. When the value of Cp increases, the number of rejects reduce dramatically. Percent defects are no longer used at higher values of Cp, instead parts per million (ppm) is used to describe the number of rejects. For example, when Cp is 1.5, rejects are 5 ppm and when Cp is 2 the rejects are 0.002 ppm (In this case process width is ± 6 and the process is called a 6<process). All the above numbers are based on the assumption that the center of the spec limits and the center of the process are the same. When this not true, Cp does not provide complete information.
where NSL is the nearest spec limit, < is the mean of the process, and the vertical lines indicate that Cpk is always a positive number. Cp and Cpk are equal for a centered process. Cpk is also useful for defining processes with single-sided specs. For example, noise figure of an amplifier has only an upper spec limit and active directivity a lower spec limit. In deriving Cpk, one should make sure that < has a meaningful value, such as between spec limits when both spec limits are present. For single-sided specs, < should be below the upper spec limit or above the lower spec limit. The graph below shows the number of rejects for various values of Cpk.
NF = 10 log
For example, if 100 and 101 MHz are the frequencies of two applied signals, then 99 and 102 MHz are the two-tone third-order products and 300 and 303 MHz are single-tone third-order products. Two-tone third-order products are very close to the desired signals and are very difficult to filter out. Hence they are of great importance in system design. In the linear region, third-order products decrease/increase by 3 dB for every 1 dB decrease/increase of input power, and output signal power decreases/increases by a dB for every dB of input power. When drawn on a X-Y graph, with input power on X-axis and output power on the Y-axis, third-order products fall on a straight line with a slope of 3 and signal power on a straight line with a slope 1 as shown below. By extending the linear portions the two lines, they intercept at a point. The X co-ordinate and the Y co-ordinate of this point are called the input and output intercept point, and the two differ by an amount equal to the small-signal gain of the amplifier. Output intercept point, IP3(dBm) can also be calculated using a simple formula. IP3(dBm)out = Pout(dBm) + A/2 where Pout (dBm) is the output power of each tone in dBm and "A" is the difference of output power and intermod level in dB. Input intercept point is obtained by substituting Pin(dBm) for Pout(dBm) in the above formula. Single-tone and two-tone third-order intercept points differ by a fixed amount but have the same slope.
## 14 Often-Asked Questions About Amplifiers
However, in many applications, the mismatch may not be objectionable. For specific performance details, the 50-ohm amplifier should be tested under 75-ohm conditions. Contact the factory or sales rep. for computer automated performance data (CAPD) on the amplifier you are considering.
First establish the 0 dB reference as follows. Apply the input signal to the directional coupler output port as shown. Apply a short circuit to the coupler's input port and measure the power at the coupled port. Then replace the short with an open circuit and note the reading at the coupled port. The average of the two readings is the 0 dB reference. Next substitute the open circuit with a 50 ohm load. Note the reading; this will give you the measurement range of the setup. Remove the 50 ohm load and replace it with the DUT. Measure how far the reflected signal is from the 0 dB reference; this is the output return loss (R.L.). To convert output return loss to VSWR, use the formula: <
Noise figure in dB = 10 log
Another common application is two-tone, third-order IM testing, where the two-tone signals must be well isolated; amplifiers with high directivity are used between source and combiner. For relatively high RF frequencies, isolators can be used but they are expensive; for frequencies below 1 GHz, they are difficult to find. High-directivity amplifiers, such as Mini-Circuits' MAN-AD series, are recommended for such applications.
Variable-gain amplifiers are available, such as Mini- Circuits' ZFL-1000G and ZFL-1000GH, to accomplish your objective.
IP2(dBm) = Pout (dBm) + A2 In the block diagram, a low-pass filter is provided to attenuate second harmonics of the generator 10 to 20 dB below that generated by the amplifier. Sufficient attenuation should be provided at the amplifier output to prevent spectrum analyzer from generating harmonics.
If F1 & F2 are the frequencies of the two tones, then 2F1 F2 and 2F2 F1 are the third-order products. The set up should ensure that second harmonic of F1 & F2 are at least 10 to 20 dB below the third-order products to be measured. Care also should be taken to prevent F1 & F2 interaction and generation of third-order products. Amplifiers 1 and 2 are selected such that they have high directivity. This provides the desired isolation of the generators. If A3 is the level of the third-order product below the desired signal, then the output third- order intercept point is given as |