shows part of a receiver system consisting of a (bandpass) filter H1 (s), a mixer and a (lowpass) filter H2(s). The output of the mixer stage is fed back to its input via an often unwanted (i.e. parasitic) feedback filter Hfb(s). In the example of the linear mixer in Fig. 4.24, this parasitic feedback path runs through the gate-source capacitances of the input transistors. It causes downconversion to baseband of the signal content in the frequency bands centered around f = 0, f = 2fo, etc. As a result, 2nd-order distortion components generated in previous stages of the receiver end up in the desired output frequency band. For the system shown in Fig. 4.28, we used SymbolicHTM to compute the expressions for the input-output HTM elements for several levels of accuracy. Here, the level of accuracy is determined by the order of the dummy variable up to which results are computed, and the number of tones taken into account. The HTM elements were evalu- ated for fo = 10MHz, H1 (s) a 4th-order maximally flat bandpass filter centered around fo with a 3 dB bandwidth of 1.5 MHz, H2(s) a 6th-order Chebyshev lowpass filter with 4.3.8 Application 2: Receiver stage with feedback across the mixing element Frequency (Hz) (a) HTM element H0,0(s) Frequency (Hz) (b) HTM element H0,2(s) Figure 4.27: Exact transfer characteristic of H0,0(s) and ,((s) (solid bold lines) and their symbolically generated components (marked lines). (a) The squared, crossed and circled line respectively correspond to the first, second and third term in equation (4.102). (b) The circled and squared line respec- tively correspond to the first and second term in equation (4.104). 4.3 AUTOMATED SYMBOLIC LPTV SYSTEM ANALYSIS Vosc cos(2ft) H1 (s) H2(s) Figure 4.28: Receiver system consisting of a bandpass filter H1 (s), a lowpass filter H2(s) and a downconversion mixer in between. The mixer output is fed back to its input via the (parasitic) feedback path Hfb (s). a passband ripple of 0.5 dB and its corner frequency at 10 kHz, and Hfb(s) a highpass filter with 