Design of minimally invasive all-pole analog lowpass filters Saiteja Damera 1 • AydınI ˙ lker Kars ¸ ılayan 1 • Jose Silva-Martinez 1 Received: 5 August 2015 / Revised: 20 January 2016 / Accepted: 10 March 2016 Ó Springer Science+Business Media New York 2016 Abstract In this paper, a new design technique for designing higher order minimally invasive lowpass filters is proposed. The proposed fully differential filter has been simulated in TSMC 130 nm technology for third and fourth orders. When compared with the conventional filter implementations such as a Tow-Thomas architecture, the proposed third order solution achieves a total in-band input-referred integrated noise of 44:09 lV compared to 78:83 lV , achieved by a Tow-Thomas implementation. The proposed solution offers higher tolerance to blockers along with lesser number of active devices required. Though, the total capacitance used is increased from 23.82 pF to 89.82 pF, from third order Tow-Thomas filter to its minimally invasive filter counterpart, the power consumption reduces by 77 % from third order Tow- Thomas to the third order minimally invasive filter. Keywords Lowpass filters  Minimally invasive  Highly linear  Blockers  Low power 1 Introduction Signal processing systems require analog filtering as a crucial element in filtering off any undesired signal or noise. Although digital implementation of filters is becoming more popular, communication systems usually require analog filters for anti-aliasing and blocker rejection. Rejecting blocker signals in the vicinity of filter’s cut-off frequency has become very crucial because the harmonic mixing of blockers can corrupt the in-band signals at low frequency drastically. For example, wireless communica- tion devices for mobile-TV applications require strong blocker rejection to relax the dynamic range of the blocks, which follow the filter in the system [1]. The main idea behind minimally invasive filter topology is to embed the filter in the signal chain in such a way that it provides minimum disturbance to the signal when it is in-band and filtering off the signal when it is out of band. Embedding the filter function into the existing analog front-end not only provides reduced overhead [2], but also allows mini- mal impact of the added filter on the in-band signals. However, conventional filter topologies strive to achieve a minimal noise and good linearity at a cost of increased area and power consumption [3–12]. Therefore, synthesizing a minimally invasive filter topology provides us with a new way of obtaining minimum noise and maximum linearity. The design of a minimally invasive filter involves the synthesis of a frequency dependent impedance which acts as a low-impedance path to ground for out-of-band signals, whereas it becomes transparent for in-band signals. The frequency dependent negative resistors (FDNR) were originally introduced in early 1970s and used in designing higher order filter topologies [13–19]. Though the filter implementation based on FDNRs offered advantages in single-ended mode, differential implementations faced several drawbacks. Also, in most of the desired low-pass realizations, the number of opamps used to realize a FDNR based filter was much higher than the number of opamps used in an integrator based conventional filter counterpart. More recently in [20], a FDNR was used to provide noise shaping techniques to shift the noise out of the passband of the filter, however at the expense of increase in power consumption. In [21], blocker rejection in a broadband RD & Saiteja Damera teja.universe@gmail.com 1 Department of Electrical and Computing Engineering, Texas A&M University, College Station, TX 77843-3128, USA 123 Analog Integr Circ Sig Process DOI 10.1007/s10470-016-0714-4