Explicit design formulas for current‐mode leap‐frog OTA‐C filters and 300 MHz CMOS seventh‐order linear phase filter

Abstract

SUMMARYThe leap-frog (LF) configuration is an important structure in analogue filter design. Voltage-mode LF OTA-C filters have recently been studied in the literature; however, general explicit formulas do not exist for current-mode LF OTA-C filters and there is also need for current-mode LF-based OTA-C structures for realization of arbitrary transmission zeros. Three current-mode OTA-C structures are presented, including the basic LF structure and LF filters with an input distributor or an output summer. They can realize all-pole characteristics and functions with arbitrary transmission zeros. Explicit design formulas are derived directly from these structures for the synthesis of, respectively, all-pole and arbitrary zero filter characteristics of up to the sixth order. The filter structures are regular and the design formulas are straightforward to use. As an illustrative example, a 300 MHz seventh-order linear phase low-pass filter with zeros is presented. The filter is implemented using a fully differential linear operational transconductance amplifier (OTA) based on a source degeneration topology. Simulations in a standard TSMC 0.18 m CMOS process with 2.5 V power supply have shown that the cutoff frequency of the filter ranges from 260 to 320 MHz, group delay ripple is about 4.5% over the whole tuning range, noise of the filter is 420 nA/ √ Hz, dynamic range is 66 dB and power consumption is 200 mW.

Performance comparison of high-order IFLF and LF linear phase lowpass OTA-C filters with and without gain boost

“…In particular, general nth-order inverse-follow-the leader-feedback (IFLF) [1,2] and leap-frog (LF) feedback OTA-C configurations have been derived. More recently, explicit design formulas for LF OTA-C filters have also been derived [8,9].…”

Programmable feedforward linearized CMOS OTA for fully differential continuous‐time filter design

“…Applications such as high-frequency continuoustime (CT) analog OTA-C filters provide solutions for various signal processing tasks [1][2][3][4][5][6][7][8][9][10][11]. In the recent years, also the field programmable analog arrays based on the tunable (programmable) OTAs 886 S. SZCZEPANSKI, B. PANKIEWICZ AND S. KOZIEL and integrating capacitors (C) have been developed successfully to built reconfigurable hardware platforms (e.g.…”

Minimum component high frequency Gm-C wavelet filters based on Maclaurin series and multiple loop feedback

“…Given a transfer function and desired specifications, different filter topologies may be suitable. It has been demonstrated that MLF Gm-C filter structures can realise transfer functions with arbitrary zeros [4,5], a feature that is particularly useful for wavelet filters since wavelet approximations often result in non-traditional zeros. MLF structures also have lower magnitude sensitivity than cascade topologies and use only grounded capacitors.…”

“…First of all, two transconductors are required in the LFF structure for realising the transmission zeros of (1), while only one transconductor is needed in the FLF structure. Also, to produce the only term in the numerator, the two transconductors in the LFF circuit need exact matching (equal values) to null an additional unwanted constant from the circuit [5]. Difference nulling is very sensitive to transistor mismatches in high frequency, which should thus be avoided in practical IC design.…”

“…First, among a number of different analogue circuits such as active-RC, log domain, switched-capacitor and switched-current, Gm-C circuits are most suitable for high frequency low power programmable applications owing to the transconductor's open loop operation, circuit simplicity and tunability [4,5], which become the obvious choice for our purpose.…”