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Chapter 5: Memoryless Nonlinearity and D... > 5.2: Signal Desensitization and Bloc... - Pg. 128

128 Chapter 5 2 2 2 1 1 1 2 1 1dBCP , P 2 , and P 1dBCP , and then the 2 R s 2 R s 2 R s relation in (5.14) implies the 1-dB compression point of the desired signal in the two-tone case occurs at lower power level than the single tone case: As defined earlier, let P 1 P 1 P 1 dBCP 2 P 2 (5.15) As a matter of fact, as the power of the interferer increases, the power of the desired signal decreases by twice the amount of the interferer power, eventually leading the desired signal to be completely blocked as will be discussed in the next section. 5.2 Signal Desensitization and Blocking When a weak desired signal is present along with a strong dominant interferer, the latter, due to the compressive behavior of the circuit, tends to reduce its overall average gain, thus serving to further weaken the desired signal. This process is known as desensitization . To illustrate this effect, consider the two-tone scenario described above where the desired tone at 1 and the interfering tone is at 2 . The output at the desired frequency can be written as: y ( t ) 1 1 3 1 3 3 1 2 2 2 1 2 cos( 1 t ) (5.16) As the interfering tone level gets larger in comparison to the desired tone level, the output at the desired signal becomes: y ( t ) 2 1 1 1 2 3 3 1 1 2 2 2 2 c os( 1 t ) 1 1 3 2 3 1 2 cos( 1 t ) 2 Gain (5.17) As discussed earlier, for compressive behavior where 3 0, the gain expression in (5.17) diminishes as the magnitude of the interfering tone 2 increases. As the desired signal gain approaches zero, the signal is said to be blocked, and the interferer is often referred to as a blocker. Signal desensitization will be further addressed in Section 5.5. w ww. n e w n e s p r e s s .c om