Active GaAs MMIC band-pass filters with automatic frequency tuning and insertion loss control

Active N-path Filters: Theory and Design

“…In fact, the addition of the negative resistance: 1) modifies the P 1dB of the circuit to P 1dB Q 0 /Q and 2) modifies the P n of the circuit to P n Q/Q 0 . Although there has been more than a decade research on these types of BPFs, most of the designs do not achieve enough DR which is to a first degree is due to the limited Q-factor of on-chip inductors [9,10,11,12,13,14,15,16,20,21,23,24,26,27,28,29,30,31,32,33]. …”

“…2.1, the negative resistance can be located in series or in parallel with the inductor. The location and the type of the negative resistance have a great impact on the passband distortion of Q-enhanced BPFs [16,20,21,23,24]. A very first-order model of an onchip inductor where only the series ohmic loss is taken into account is shown in Fig.…”

“…It can be shown that the DR of a 2 nd order Q-enhanced LC BPF shown in Frequency dependent negative resistors [16] (c) A series LC tank with a constant series negative resistance [20] (d) A parallel LC tank with a constant negative resistance in series with its inductor [21] (e) A modified differential negative resistance [21,24]. …”

“…A popular method for tuning the Q-factor and the center frequency of the Q-enhanced LC filters is shown in Fig. 2.6 [9,16,23,34,35]. As can be seen, it is based on an indirect automatic tuning of the filter (Fig.…”

“…These filters were typically off-chip, bulky and expensive which led to penalties in terms of cost, form factor and less design flexibility. The push towards single-chip solutions led to a tremendous amount of research on the integration of these bandpass filters [9,10,11,12,13,14,15,16]. Analog BPFs have been notoriously difficult to implement on-chip.…”