CMOS Realization of VDVTA and OTA Based Fully Electronically Tunable First Order All Pass Filter with Optimum Linearity at Low Supply Voltage ± 0.85 V

This paper presents a new first order all pass filter configurations. The proposed all pass filter configuration employs two configurations namely VDVTA and OTAs based first order all pass filter configuration. The first proposed configuration employs a single VDVTA and one grounded capacitor whereas the second proposed configuration employs two OTAs and one grounded capacitor. Both types of proposed configurations are fully electronically tunable and their quality factors do not depend on tunable pole frequency range. The reported configurations yield low active and passive sensi-tivities and also have low power consumption with very low supply voltage ± 0.85 V with Bias Voltage ± 0.50 V. The PSPICE simulation of the proposed VDVTA and two OTAs based first order all pass filter configurations are verified using 0.18 µm CMOS Technology Process Parameters.


Introduction
Due to recent development in the fields of microelectronics, analog signal processing as well as digital signal processing and all the fields of communication, size of the transistors and power supplies are reduced. Last few decades, current mode active building blocks have been evolved in the realization of ac-tive filters and oscillators. Current mode building blocks have higher bandwidth, higher dynamic range and higher slew rate with low power consumption. First order all pass filter and higher order filters are widely used in the fields of analog signal processing, measurement, instrumentation, voice or audio frequency range. The magnitude characteristics play vital role due to insensitivity of ear and Biomedical applications. Recently, most widely active building blocks are used in the designing oscillators, grounded Inductor and active filter applications. These active building blocks namely operational Amplifier, Current-mode current, gain first-order all pass filters employing CFTAs [1], A voltage-mode first order all pass filter based on VDTA [2], Voltage-mode all-pass filters including minimum component count circuits [3], Voltage-mode cascadable all-pass section using single active element [4], Single VDVTA Based Voltage-Mode Biquad Filter [5], Single MO-CCCCTA-Based Electronically Tunable Current/Trans-Impedance-Mode Biquad Universal Filter [6], Electronically Tunable Low Voltage Mixed-Mode Universal Biquad Filter [7], Current-tunable current-mode all-pass section using DDCC [8], Electronically tunable first-order all pass section using OTAs [9], Current-mode multi phase sinusoidal oscillator using CDTA-based all pass sections [10], New resistorless and electronically tunable realization of dual-output VM all-pass filter using VDIBA [11], Cascadable Current-mode first order all-pass filter based on minimal components [12], Voltage-mode all-pass filters using universal voltage conveyor and MOSFET-based electronic Resistors [13], Voltage mode cascadable all-pass sections using single active element and grounded passive components [14], Electronically tunable first-order all-pass circuit employing DVCC [15], Novel voltage-mode all-pass filter based on using DVCCs [16], A Resistorless realization of the first-order all-pass filter [17], High input impedance voltage-mode first-order all-pass sections [18], Unity/variable-gain voltage-mode/current-mode first-order all-pass filters using single DXCCII [19], First-order voltage-mode all-pass filter employing one active element and one grounded capacitor [20], Component reduced all-pass filter with a grounded capacitor and high-impedance input [21], Realization of Grounded Inductor Based Band Pass Filter Design to Achieve Optimum Linearity with Bandwidth using Single VDVTA [22], Multi output filter and four phase sinusoidal oscillator using CMOS DX-MOCCII [23], FDCCII based Electronically Tunable Voltage Mode Biquad Filter [24], CDBA Based Inverse Filter [25].

Description of the Proposed Active Building Blocks VDVTA and OTA for First Order All Pass Filter
The symbolical representation of the VDVTA as an active element is shown in Figure 1 contains three input terminals namely P, N, V and Z, X + , X − are output terminals. All input terminals and output terminals exhibit high impedance values. The symbolic representation of OTA is shown in Figure 2(a) and Figure   2(b) represents Equivalent Circuit of OTA respectively. The symbolical representation of the VDVTA as an active element is shown in Figure 1 contains three input terminals namely P, N, V and Z, X + , X − are output terminals. All The currents x I + , x I − and z I are characterized by the Equations (1.1). ( The transfer functions of transadmittance mode all pass filter are employed single VDVTA with one grounded capacitor is shown in Figure 3 and two OTAs with one grounded capacitor is shown in Figure 4.   The transfer functions of transadmittance mode all pass filter is given in Equ- The proposed transimpedance mode all pass filter using two OTAs.
OTAs contains high impedance input terminals and the implementation of the proposed transimpedance mode all pass filter using single VDVTA and one grounded capacitor respetively.
Transfer function of proposed OTAs based all pass filter is characterized by the Equation (2.2): The phase margin and gain of the proposed all pass filters using two VDVTA and OTAs can be described in Equation (2.3):

CMOS Simulation Result
The CMOS Simulation result shows that the workability and functionality of the         Table 3. are taken from TMSC 0.18 μm CMOS technology parameters at ±0.5 V supply voltages all gm equal to 639.7 μA/V or 734 μA/V are used for the proposed VDVTA and OTAs based first order all pass filters yield high linearity.

Performance Evaluation
The performance of the proposed VDVTA and OTAs based first order all pass Figure 11. Simulated frequency response with phase of proposed all pass filter.

Conclusions
The workability and functionality of the proposed OTAs and VDVTA based all pass filter are verified with CMOS simulation in the SPICE 0.18 um CMOS Technology. In an analog Signal Processing, first order all pass filter is widely used to shift the phase of input signal.
The reported OTAs and VDVTA based all pass filter yields some advantageous features: 1) Fully integrated with monolithic ICs.
2) Electronic tunability with different pole frequencies at different bias currents.
3) The proposed VDVTA based all pass filter configuration exhibits low input impedance and high output impedance.
4) The proposed VDVTA based all pass filter configuration exhibits good sensitivity performance. 5) The reported work represents wideband bulk-driven OTA with tunable transconductance was designed.
6) The natural frequency (ω 0 ) of the reported OTAs and VDVTA based all pass filter can be tuned with g m2 or gm 2 and with capacitor C2 at constant bandwidth. 7) Bandwidth can be controlled with the help of transconductance (g m1 ) and quality factor (Q) can be controlled independent of natural frequency (ω 0 ) with transconductance (g m1 ).
8) For the first configuration using single VDVTA, we can change cut off frequency or pole frequency by changing g m . 9) Whereas in second configuration OTAs based all pass filter, the cut off frequency or pole frequency can be changed by tuning g m1 or g m2 .
10) The integration of proposed OTA and VDVTA based first order all pass filter is open area in future research using modern mixed analog signal processing based integrated circuits for achieving high linearity at low voltage.