Reduction size and power consumption is very important for the design of wearable and implantable medical devices since compact physical space and long battery lifetime are the major concerns nowadays.
Continuous-time low pass filter (LPF) is an essential building block for biopotential sensor interface or the front-end part of the devices mentioned above. It exists for anti-aliasing and signal discrimination simultaneously. Dealing with biopotentials that acquire frequencies ranging from dc to 10 kHz , realizing large time constants within a reasonable chip area is challenging. In CMOS technology, sub threshold devices are popular for the design of such a filter for the following reasons. First, when power consumption is concerned, the sub threshold devices can conduct very low currents in the range of a few microamps down to several tens of pico amp. This creates the possibility to operate the filter with a few nanowatts of power. The second reason concerns the chip area. The very low sub threshold currents lead to sufficiently low trans conductances that allow large time constants to be implemented within a reasonable on-chip space.
Regarding the filter topology, the most compact and power efficient structure is always preferred. Exploiting a single transistor as an active element without linearization and fitting it into a single-branch or current-reuse structure is indeed a compact and low-power solution. The source-follower biquads are early examples of this design approach. They can be extended by adding a couple of capacitors to form a zero-pole transfer function . Incorporation with transistorized active inductors, very compact and power-efficient bandpass and LC-ladder lowpass filters have been made successfully in and, respectively. A single-branch LPF designed to obtain a very large tuning range (kHz to GHz) has also been reported . The other variations further developed from the source-follower filter for high frequency applications can also be found .
For low-frequency applications, the source follower biquads have also been directly employed in for the design of a biopotential LPF using MOS devices operated in weak inversion. The LPF, formed by cascading the biquads, contains complementary devices making it suffer from the bulk effect that attenuates the filter’s passband gain, if fabricated in a standard CMOS technology. To enhance the passband gain, a compensation network needs to be inserted . Although this solution can be made successfully without additional power consumption, it complicates the filter topology and design procedure.
More recent single-branch biquads are reported using a flipped voltage follower (also called ‘self-coupled source follower’ in and ‘flipped source follower’ in). Employing these cells, a LPF can be designed to operate from a supply voltage and consume power less than the LPF of . Unfortunately, realizing a cascaded LPF using these types of biquads also involves complimentary devices. Therefore, the pass band attenuation induced by the bulk effect is again unavoidable for standard CMOS fabrication. summarizes the relevant features of all the filters mentioned above. It also reveals the common drawback of the filters that the bulk effect attenuates their passband responses.
This paper tackles the aforementioned problem by introducing two current-reuse CMOS biquads so that their problems of bulk effect can be neutralized . Surprisingly, this can be made by introducing the bulk effect to all transistors in the filter core of each biquad. However, traditional way of connecting the bulk terminal of each transistor to its own substrate, passband attenuation can also be nullified by cascading different types of the biquad for a higher-order LPF design. The two proposed biquads are employed to implement a 4thorder LPF in 0.35 μm CMOS technology. The proposed LPF serves electrocardiography (ECG) acquisition that requires a dynamic range (DR) and cutoff frequency ( fC) of 45 dB and 250 Hz, respectively . With power consumption of a few nano watts, the LPF can satisfy the requirements mentioned above with the best figure of merit (FoM) compared with other designs existed in the same category.
- More area occupied.
- More power Consumption.
In recent technology of biomedical applications will enhanced performance in day by day digital humanity, thus it will have lot of medical diplomacy such as wearable health monitoring systems, heart attacks early prediction devices, seizure predictions devices and so on. In recent technology in the direction of improved this medical devices with more efficient in power consumption, long battery life, minimum area, and input signals accuracy. In this proposed work of nanopower CMOS 4th order low pass filter is very appropriate for this biomedical applications, thus it will reduce the signal tolerance, fluctuation in all type of ECG, EMG signals, here this proposed work presents to design a biopotential low pass filter with sub threshold two differential Biquads method at 45nm CMOS technology, which presents in TANNER EDA tool and finally it will proved better in all the comparisons in terms of area, delay and power to compared existing method of 130nm CMOS technology of Biopotential low pass filter.
- Less area occupied.
- Less power Consumption.