14.4 nW fourth-order bandpass filter for biomedical applications

A 2.6nW, 0.5V, 52dB-DR, 4^th-order G<inf>m</inf>-C BPF: Moving closer to the FoM's fundamental limit

“…The results are shown in Table 1. The main distinct features of our design are the 0.5 V V DD and the FoM of 0.063×10 -13 which is more than an order of magnitude better than that of [4], the lowest number reported until recently. The BPF of [4] and ours are comparable in circuit complexity and process technology but the pMOS 2 nd -order circuit cell of [4] cannot be connected in cascade without considerable loading effect and the circuit itself requires a higher V DD of 2V SG +V SDsat .…”

“…In [4], a simple cascade topology (which has also been used in [1]) formed by a compact G m -C biquad structure adapted from [6] was employed while the BPF of [5] uses conventional differential pair transconductors to simulate a ladder passive LC prototype. Compared to the fundamental limit for V DD = 1V, we can see that the FoM of [4] is still more than 6 orders of magnitude away from the fundamental limit.…”

“…In this paper, we develop further to achieve more than one order of magnitude FoM improvement with respect to [4]. This can be done by inventing a 2 nd -order filter topology that is able to operate from a lower supply voltage and can be cascaded without the expense of a voltage buffer and be fit into a power-efficient single branch circuit structure that uses a single transistor as the transconductance element.…”

“…Fig. 2a shows the 2 nd -order BPF topology used in [1] and [4]. Capacitor C 1 with transconductor G m1 and C 2 with G m2 form the high-pass and low-pass cutoff sections, respectively.…”

“…For higher order realization, a cascade connection of this circuit is required. Unfortunately, to prevent any loading effect, a voltage follower is needed to be inserted in front of [4]. This leads to more chip area and power consumption.…”