A 2-v/sub pp/ 80-200-mhz fourth-order continuous-time linear phase filter with automatic frequency tuning

Abstract

A CMOS 80-200-MHz fourth-order continuous-time 0.05 equiripple linear phase filter with an automatic frequency tuning system is presented. An operational transconductance amplifier based on transistors operating in triode region is used and a circuit that combines common-mode feedback, common-mode feedforward, and adaptive bias is introduced. The chip was fabricated in a 0.35-m process; filter experimental results have shown a total harmonic distortion less than 44 dB for a 2-V pp differential input with a single 2.3-V power supply. The group delay ripple is less than 4% for frequencies up to 1.5. The frequency tuning error is below 5%.

A 12-mW 264-MHz high linearity sharp roll-off CMOS opamp-RC low-pass filter for MB-OFDM UWB systems

“…The LPF performance of this work is summarized in Table 1 and is compared with previously reported works of high frequency LPF designs in Table 2. Based on the defined figure of merit (FOM) in [18,19], a modified FOM is proposed (9) to provide an accurate comparison of the performance of the designed LPF with previous publications. Since the pole's frequency is proportional to the transconductance which is proportional to the square-root of the bias current, doubling the bandwidth requires 4 times increase of current.…”

“…These limitations can be overcome with active-RC LPF approach. However, previously reported works of active-RC LPF are often for narrow band applications and most papers show the cutoff frequency in the range of a hundred MHz are G m -C type [8][9][10][11][12]. It is due to the open-loop structure and excellent gain-bandwidth property of G m -C integrator.…”

Dynamic modeling of tunable analog integrated filters for a stability study of on-chip automatic tuning loops

“…This typically leads to the design of controllers that consist of a dominant pole with a high DC gain, which should ideally both ensure a sufficient phase margin and minimize the steady-state error. Therefore, one common practice is to consider a controller given by an integrator with a single pole at the origin [3,14,15,[17][18][19], expressed as:…”

“…A considerable number of practical implementations of continuous time filters with tuning loops have been presented [5][6][7][8][9][10][11][12][13][14][15][16]. Nevertheless, in spite of the wide use of these circuits, the design-oriented analysis and modeling of filter tuning structures is scarce in the literature, although the stability study of tuning loops is considered as one of the problems yet to be resolved in these systems [17].…”

“…The usual approach for overcoming instability problems is to compensate loops with low-frequency dominant pole characteristics (integral controller) [3,14,15,[17][18][19]. Using this integral controller, stability can be assured to the detriment of high bandwidth operation of the tuning loops.…”