An irksome 2nd-order spurious response called the half-IF (1/2 IF) spurious response, is defined for the mixer indices of (m = 2, n = -2) for low-side injection and (m = -2, n = 2) for high-side injection. For low-side injection, the input frequency that creates the half-IF spurious response is located below the desired RF frequency by an amount fIF/2 from the desired RF input frequency. The desired RF frequency is represented by 2400 MHz, and in combination with the LO frequency of 2200 MHz, the resulting IF frequency is 200MHz. For this example, the undesired signal at 2300 MHz causes a half-IF spurious product at 200MHz. For high-side injection, the input frequency that creates the half-IF spurious response is located above (by fIF/2) the desired RF. Note that high side injection implies that the LO frequency is above the RF frequency and low side injection implies that the LO frequency is below the RF frequency.

The second order intercept point is used to predict the mixer performance with respect to the half IF spurious response. For further details please see the article under engineer’s corner/engineering pages in our website at www.signalpro.biz.