Design and Verification of a New Universal Active Filter Based on the Current Feedback Operational Amplifier and Commercial AD844 Integrated Circuit

This paper presents a triple-input and four-output type voltage-mode universal active filter based on three current-feedback operational amplifiers (CFOAs). The filter employs three CFOAs, two grounded capacitors, and six resistors. The filter structure has three high-input and three low-output impedances that simultaneously provide band-reject, high-pass, low-pass, and band-pass filtering functions with single-input and four-output type and also implements an all-pass filtering function by connecting three input signals to one input without the use of voltage inverters or switches. The same circuit configuration enables two unique filtering functions: low-pass notch and high-pass notch. Three CFOAs with three high-input and low-output impedance terminals enable cascading without voltage buffers. The circuit is implemented using three commercial off-the-shelf AD844 integrated circuits, two grounded capacitors, and six resistors and further implemented as a CFOA-based chip using three CFOAs, two grounded capacitors, and six resistors. The CFOA-based chip has lower power consumption and higher integration than the AD844-based filter. The circuit was simulated using OrCAD PSpice to verify the AD844-based filter and Synopsys HSpice for post-layout simulation of the CFOA-based chip. The theoretical analysis is validated and confirmed by measurements on an AD844-based filter and a CFOA-based chip.


Introduction
In electrical circuits and systems, filters play an essential role in sensors and signal processing and have received considerable attention in recent years because signals acquired through sensing elements must be filtered out of external noise using filters [1][2][3][4][5][6].The technical literature [7] describes a conceptual scheme for sensing applications in phase-sensitive detection technology, where two low-pass (LP) filters are used to select the frequency range and eliminate out-of-band noise from the sensor device signal.For sensors, instrumentation and measurement systems, and electrical systems, filters reduce external noise, eliminate interference, improve signal quality, and maintain signal integrity [8][9][10].
Active circuits with high-performance characteristics are of great interest [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], especially the AD844AN integrated circuit (IC) using CFOA, which is beneficial to rapid verification of the designed circuits [27][28][29][30][31]. Typically, the voltage-mode universal secondorder filters can realize all-pass (AP), band-reject (BR), high-pass (HP), LP, and band-pass (BP) filtering functions by properly selecting different input signals.In contrast, the voltagemode multifunction second-order filters can simultaneously realize HP, LP, and BP filtering functions [32].Two unique filtering functions, low-pass notch (LPN) and high-pass notch (iv) Three high-input and low-output impedances are suitable for cascading voltage-mode operation capability without voltage buffers.(v) Simultaneously realize the voltage-mode second-order LP, BP, HP, and BR filtering functions without requiring component matching conditions.(vi) No capacitance is connected in series at terminal X of the CFOA.(vii) No voltage inverter is required for the AP filtering function.(viii) The filter parameters of resonance angular frequency (ω o ) and quality factor (Q) independently control the particular case.(ix) The circuit has low active and passive sensitivity performance.(x) Integrate the voltage-mode UAF into a single CFOA-based chip.
Table 1 compares the proposed voltage-mode UAF and the previous CFOA-based biquadratic filters [32][33][34][35][36][37][38][39][40][41][42][43].The proposed CFOA-based voltage-mode UAF simultaneously satisfies all of the tenth properties.In addition, the circuit is further implemented in a single CFOA-based voltage-mode UAF chip with lower power consumption and higher integration than the AD844-based filter.Compared to CFOA-based voltage-mode filters in the recent technical literature [39][40][41][42][43], the proposed CFOA-based voltage-mode UAF does not require any switch and achieves LP, BP, HP, BR, LPN, HPN, and AP filtering functions from the same configuration.Moreover, the circuit simultaneously realizes LP, NP, HP, and BR filtering functions.The CFOA-based voltage-mode UAF chip is manufactured with TSMC 180 nm 1P6M CMOS process technology, featuring low power consumption and high integration.Measurements using three commercial off-the-shelf AD844AN ICs and a CFOA-based voltage-mode UAF chip validate and confirm the theoretical analysis.

Circuit Descriptions and Realizations
The ideal CFOA is a four-port active component with two input ports, X and Y, and two output ports, Z and W, as shown in Figure 1.The port relations of CFOA can be characterized by V X = V Y , V W = V Z , I Y = 0, and I X = I Z [43].The ideal CFOA is logically representable as a voltage buffer between the Y and X terminals, a current follower between the X and Z terminals, and a subsequent voltage buffer between the Z and W ports.Moreover, CFOA can be implemented in hardware using commercially available off-the-shelf AD844AN IC [44].

Circuit Descriptions and Realizations
The ideal CFOA is a four-port active component with two input ports, X and Y, and two output ports, Z and W, as shown in Figure 1.The port relations of CFOA can be characterized by VX = VY, VW = VZ, IY = 0, and IX = IZ [43].The ideal CFOA is logically representable as a voltage buffer between the Y and X terminals, a current follower between the X and Z terminals, and a subsequent voltage buffer between the Z and W ports.Moreover, CFOA can be implemented in hardware using commercially available off-the-shelf AD844AN IC [44].
The circuit symbol of an ideal CFOA.

Proposed Voltage-Mode UAF Configuration
The proposed voltage-mode UAF configuration is shown in Figure 2, which consists of three CFOAs, two grounded capacitors, and six resistors.In Figure 2, the input signals Vi1, Vi2, and Vi3 are connected to the high input terminal of each Y terminal of the three CFOAs.The output voltages Vo1, Vo2, and Vo3 are connected to the low output terminal of each W terminal of the three CFOAs.High-input and low-output impedances can be used for cascaded voltage-mode operation without requiring any voltage buffers.Routine analysis of the voltage-mode UAF in Figure 2 gives the following four output voltages: The proposed voltage-mode UAF configuration.
Figure 1.The circuit symbol of an ideal CFOA.

Proposed Voltage-Mode UAF Configuration
The proposed voltage-mode UAF configuration is shown in Figure 2, which consists of three CFOAs, two grounded capacitors, and six resistors.In Figure 2, the input signals V i1 , V i2 , and V i3 are connected to the high input terminal of each Y terminal of the three CFOAs.The output voltages V o1 , V o2 , and V o3 are connected to the low output terminal of each W terminal of the three CFOAs.High-input and low-output impedances can be used for cascaded voltage-mode operation without requiring any voltage buffers.Routine analysis of the voltage-mode UAF in Figure 2 gives the following four output voltages: Sensors 2023, 23, x FOR PEER REVIEW 6 of 30

Circuit Descriptions and Realizations
The ideal CFOA is a four-port active component with two input ports, X and Y, and two output ports, Z and W, as shown in Figure 1.The port relations of CFOA can be characterized by VX = VY, VW = VZ, IY = 0, and IX = IZ [43].The ideal CFOA is logically representable as a voltage buffer between the Y and X terminals, a current follower between the X and Z terminals, and a subsequent voltage buffer between the Z and W ports.Moreover, CFOA can be implemented in hardware using commercially available off-the-shelf AD844AN IC [44].
The circuit symbol of an ideal CFOA.

Proposed Voltage-Mode UAF Configuration
The proposed voltage-mode UAF configuration is shown in Figure 2, which consists of three CFOAs, two grounded capacitors, and six resistors.In Figure 2, the input signals Vi1, Vi2, and Vi3 are connected to the high input terminal of each Y terminal of the three CFOAs.The output voltages Vo1, Vo2, and Vo3 are connected to the low output terminal of each W terminal of the three CFOAs.High-input and low-output impedances can be used for cascaded voltage-mode operation without requiring any voltage buffers.Routine analysis of the voltage-mode UAF in Figure 2 gives the following four output voltages: The proposed voltage-mode UAF configuration.According to (1)-( 4), when the two input voltages of V i1 and V i2 are grounded, and V i3 is provided as the input signal of V in , four different filtering functions can be realized simultaneously.
From ( 5) to (8), the filter parameters bandwidth (BW), ω o , Q, passband gain a 1 and a 2 , and BR frequency ω z are given by (11) Based on (5) to (7), an inverting band-pass (IBP) filtering function with R 1 /R 2 passband gain is obtained at V o1 , a non-inverting LP (NLP) filtering function with unity passband gain is obtained at V o2 , and a non-inverting HP (NHP) filtering function with R 1 /R 2 passband gain is obtained at V o3 .According to (8), the following three BR filtering functions are obtained.
(a) If R 1 = R 2 and R 5 = R 6 , the regular BR filtering function with 1/2 passband gain can be realized in (12).
(b) If R 5 < R 6 and ω z > ω o , the LPN filtering function can be obtained in (8).
(c) If R 5 > R 6 and ω z < ω o , the HPN filtering function can also be obtained in (8).
By connecting three input signals of V i1 , V i2 , and V i3 into one input signal and selecting the matching element condition of R 1 = R 2 and C 1 R 3 = 2C 2 R 4 , the voltage-mode UAF of V o3 performs the following non-inverting AP (NAP) filtering function.
According to (9), the voltage-mode UAF parameters BW, ω o, and Q can be controlled orthogonally by R 1 = R 3 = R a .In this particular case, (9) becomes Equation ( 14) expresses that R a independently controls the parameters BW and Q without affecting the parameter ω o .When R 3 = R 4 = R b , the parameters ω o and Q in (9) become Equation ( 15) expresses that R b independently controls the parameter ω o without affecting the parameter Q. Equations ( 14) and (15) show that the voltage-mode UAF parameters Q and ω o are independently controlled by R a and R b , respectively.
The voltage-mode UAF parameters ω o and Q, in the case of non-ideal CFOA terminal characteristics, are According to the definition of [43], the active and passive sensitivity parameters ω o and Q of voltage-mode UAF are calculated as follows. S From the results, the voltage-mode UAF exhibits low active and passive sensitivities.If V i1 and V i2 are grounded, and only V i3 is provided as the input signal of V in , the four different filtering functions for non-ideal voltage and current gains become The CFOA terminal characteristics generally have various parasitic impedances [43].The parasitic impedances of these non-ideal CFOAs can affect the performance of the proposed voltage-mode UAF. Figure 3 illustrates the non-ideal CFOA model for analyzing the parasitic impedances and their effect on the voltage-mode UAF configuration.Using the CFOA non-ideal model, the parasitic impedance effect of the proposed voltage-mode UAF is analyzed, as shown in Figure 4. Reanalyzing the voltage-mode UAF in Figure 4, the following non-ideal four output node voltages are obtained: The effect of CFOA parasitic resistances and capacitances on the voltage-mode UAF configuration.
Equations ( 26)-(29) show that several parasitic resistances of RX1, RX2, RX3, RZ1, RZ2, and RZ3 and three parasitic capacitances of CZ1, CZ2, and CZ3 will affect the voltage-mode UAF.In Figure 4, the proposed voltage-mode UAF has the attractive advantage that capacitors C1 and C2 are grounded, and resistors R2, R3, and R4 are connected to the X-terminal of the CFOA, respectively.The main advantage of the proposed voltage-mode UAF topology is that the two parasitic capacitance effects of CZ1 and CZ2 can be absorbed by the two grounded capacitors of C1 and C2, and the three parasitic resistances of RX1, RX2, and RX3 can also be absorbed by three series resistors of R3, R4, and R2, respectively.It is worth noting that the parasitic capacitance CZ3 and the parasitic resistances RZ1, RZ2, and RZ3 affect the operating frequency range of voltage-mode UAF.If the conditions of s(C1 + CZ1) >> 1/RZ1, s(C2 + CZ2) >> 1/RZ2, and sCZ3(R1//RZ3) << 1 are satisfied, the influence of the parasitic resistances and capacitances on voltage-mode UAF topology can be reduced.Therefore, The effect of CFOA parasitic resistances and capacitances on the voltage-mode UAF configuration.
Equations ( 26)-(29) show that several parasitic resistances of RX1, RX2, RX3, RZ1, RZ2, and RZ3 and three parasitic capacitances of CZ1, CZ2, and CZ3 will affect the voltage-mode UAF.In Figure 4, the proposed voltage-mode UAF has the attractive advantage that capacitors C1 and C2 are grounded, and resistors R2, R3, and R4 are connected to the X-terminal of the CFOA, respectively.The main advantage of the proposed voltage-mode UAF topology is that the two parasitic capacitance effects of CZ1 and CZ2 can be absorbed by the two grounded capacitors of C1 and C2, and the three parasitic resistances of RX1, RX2, and RX3 can also be absorbed by three series resistors of R3, R4, and R2, respectively.It is worth noting that the parasitic capacitance CZ3 and the parasitic resistances RZ1, RZ2, and RZ3 affect the operating frequency range of voltage-mode UAF.If the conditions of s(C1 + CZ1) >> 1/RZ1, s(C2 + CZ2) >> 1/RZ2, and sCZ3(R1//RZ3) << 1 are satisfied, the influence of the parasitic resistances and capacitances on voltage-mode UAF topology can be reduced.Therefore, Equations ( 26)-(29) show that several parasitic resistances of R X1 , R X2 , R X3 , R Z1 , R Z2 , and R Z3 and three parasitic capacitances of C Z1 , C Z2 , and C Z3 will affect the voltagemode UAF.In Figure 4, the proposed voltage-mode UAF has the attractive advantage that capacitors C 1 and C 2 are grounded, and resistors R 2 , R 3 , and R 4 are connected to the X-terminal of the CFOA, respectively.The main advantage of the proposed voltage-mode UAF topology is that the two parasitic capacitance effects of C Z1 and C Z2 can be absorbed by the two grounded capacitors of C 1 and C 2 , and the three parasitic resistances of R X1 , R X2 , and R X3 can also be absorbed by three series resistors of R 3 , R 4 , and R 2 , respectively.It is worth noting that the parasitic capacitance C Z3 and the parasitic resistances R Z1 , R Z2 , and R Z3 affect the operating frequency range of voltage-mode UAF.If the conditions of s(C 1 + C Z1 ) >> 1/R Z1 , s(C 2 + C Z2 ) >> 1/R Z2 , and sC Z3 (R 1 //R Z3 ) << 1 are satisfied, the influence of the parasitic resistances and capacitances on voltage-mode UAF topology can be reduced.Therefore, the valid operating frequency range of the voltage-mode UAF needs to be considered as follows.
According to (30), the non-ideal three output node voltages of ( 26) to ( 28) are simplified as In this case, the three non-ideal voltage transfer functions, the denominator D n (s), and the non-ideal filter parameters of ω on and Q n were obtained as If V i1 and V i2 are grounded, and only V i3 is provided as the input signal of V in , the four different filtering functions for non-ideal voltage outputs become As shown in (30), the voltage-mode UAF must operate within the effective operating frequency range to minimize the effects of the non-ideal CFOA parasitic resistances and capacitances.

Simulation and Experimental Results
The proposed voltage-mode UAF efficiency and flexibility were demonstrated using commercially available off-the-shelf AD844AN ICs and on-chip design measurements to validate the theoretical analysis.

The AD844-Based Voltage-Mode UAF Simulation and Measurement Results
The passive components of the AD844-based voltage-mode UAF are selected as C1 = C2 = 100 pF and Ri = 10 kΩ (i = 1 to 6) with a resonance frequency of fo = 159.15kHz.Regarding the AD844 datasheet [44], the X terminal parasitic resistance of AD844 is RX = 50 Ω.The Z terminal parasitic resistance and parasitic capacitance of AD844 are RZ = 3 MΩ and CZ = 4.5 pF, respectively.According to (30), the effective operating frequency range of the AD844-based voltage-mode UAF is 1.74 kHz to 885.37 kHz. Figure 7 shows the simulated frequency spectrum of the IBP filtering response at Vo1.As shown in Figure 7, the total harmonic distortion (THD) is calculated as 0.6% for a sinusoidal input voltage of 2.4

The AD844-Based Voltage-Mode UAF Simulation and Measurement Results
The passive components of the AD844-based voltage-mode UAF are selected as C1 = C2 = 100 pF and Ri = 10 kΩ (i = 1 to 6) with a resonance frequency of fo = 159.15kHz.Regarding the AD844 datasheet [44], the X terminal parasitic resistance of AD844 is RX = 50 Ω.The Z terminal parasitic resistance and parasitic capacitance of AD844 are RZ = 3 MΩ and CZ = 4.5 pF, respectively.According to (30), the effective operating frequency range of the AD844-based voltage-mode UAF is 1.74 kHz to 885.37 kHz. Figure 7 shows the simulated frequency spectrum of the IBP filtering response at Vo1.As shown in Figure 7, the total harmonic distortion (THD) is calculated as 0.6% for a sinusoidal input voltage of 2.4

The AD844-Based Voltage-Mode UAF Simulation and Measurement Results
The passive components of the AD844-based voltage-mode UAF are selected as C 1 = C 2 = 100 pF and R i = 10 kΩ (i = 1 to 6) with a resonance frequency of f o = 159.15kHz.Regarding the AD844 datasheet [44], the X terminal parasitic resistance of AD844 is R X = 50 Ω.The Z terminal parasitic resistance and parasitic capacitance of AD844 are R Z = 3 MΩ and C Z = 4.5 pF, respectively.According to (30), the effective operating frequency range of the AD844-based voltage-mode UAF is 1.74 kHz to 885.37 kHz. Figure 7 shows the simulated frequency spectrum of the IBP filtering response at V o1 .As shown in Figure 7, the total harmonic distortion (THD) is calculated as 0.6% for a sinusoidal input voltage of 2.4 V pp .Figure 8 shows the measured frequency spectrum of the IBP filtering response at V o1 .As shown in Figure 8, the THD is calculated as 1.68% for a sinusoidal input voltage of 5.2 V pp, and the measured spurious-free dynamic range is 37.According to (14), R 1 = R 3 = R a can independently control the Q value in the AD844-based voltage-mode UAF without affecting the parameter ω o .Thus, with fixed C 1 = C 2 = 300 pF and R 2 = R 4 = 4 kΩ, the required R a values are 3.2 kΩ, 5.44 kΩ, 7.68 kΩ, and 10 kΩ for selected Q values of 0.8, 1.36, 1.92, and 2.5, respectively.Figures 21-23 show the behavior of the AD844-based VM-UAF quality factor independently controlled by R a when V i3 = V in and V i1 = V i2 = 0.According to (15), R 3 = R 4 = R b can independently control the resonance frequency value in the AD844-based voltage-mode UAF without affecting the parameter Q.Thus, with fixed C 1 = C 2 = 100 pF and R 1 = R 2 = 10 kΩ, the required R b values are 50 kΩ, 24 kΩ, 12 kΩ, and 6 kΩ for selected resonant frequency values of 31.83kHz, 66.31 kHz, 132.62 kHz, and 265.26 kΩ, respectively.Figures 24-26 show the behavior of the AD844based voltage-mode UAF resonant frequency f o independently controlled by R b when V i3 = V in and V i1 = V i2 = 0.As shown in Figures 23 and 26, simulations and measurements confirm the theoretical analysis according to (14) and (15).

The On-Chip CMOS VM-UAF Simulation and Measurement Results
Passive components of the on-chip CMOS CFOA-based voltage-mode UAF are designed as C1 = C2 = 15 pF and Ri = 20 kΩ (i = 1 to 6) with a resonance frequency of fo = 530.5 kHz. Figure 27 shows the overall layout of the CFOA-based voltage-mode UAF and its chip micrograph with two CFOA-based voltage-mode UAFs.The CMOS implementation of CFOA is shown in Figure 28 [40].In Figure 28, the length (L) and width (W) of transistors M1 to M16 are 0.4 μm and 75 μm, the L and W of transistors M17 to M20 are 0.8 μm and 13 μm, and the L and W of transistors M21 to M28 are 0.4 μm and 26 μm. Figure 29 shows the simulated frequency spectrum of the IBP filtering response at Vo1.As shown in Figure 29, the THD is calculated as 0.25% for a sinusoidal input voltage of 0.4 Vpp. Figure 30 shows the measured frequency spectrum of the IBP filtering response at Vo1.As shown in Figure 30, the THD is calculated as 1% for a sinusoidal input voltage of 0.4 Vpp, and the  Figure 29 shows the simulated frequency spectrum of the IBP filtering response at V o1 .As shown in Figure 29, the THD is calculated as 0.25% for a sinusoidal input voltage of 0.4 V pp .Figure 30 shows the measured frequency spectrum of the IBP filtering response at V o1 .As shown in Figure 30, the THD is calculated as 1% for a sinusoidal input voltage of 0.4 V pp , and the measured spurious-free dynamic range is 43.55 dBc.

Conclusions
Three voltage-mode UAFs based on CFOA have been proposed in the technical literature, using four CFOAs, two grounded capacitors, five/six resistors, and one/two switches [43].This study proposes a new voltage-mode UAF to improve the convenience and versatility of the recently introduced three voltage-mode UAF circuits [43].The pro-

)Figure 3 .
Figure 3.The effect of parasitic resistances and capacitances on ideal CFOA.

Figure 3 .Figure 3 .
Figure 3.The effect of parasitic resistances and capacitances on ideal CFOA.

Figure 4 .
Figure 4.The effect of CFOA parasitic resistances and capacitances on the voltage-mode UAF configuration.

Figure 7 .
Figure 7.The simulated frequency spectrum for the AD844-based voltage-mode UAF at Vo1 IBP filter.

Figure 8 .
Figure 8.The measured frequency spectrum for the AD844-based voltage-mode UAF at Vo1 IBP filter, where # is the reference symbol.

Figure 7 .Figure 7 .
Figure 7.The simulated frequency spectrum for the AD844-based voltage-mode UAF at V o1 IBP filter.

Figure 8 .
Figure 8.The measured frequency spectrum for the AD844-based voltage-mode UAF at Vo1 IBP filter, where # is the reference symbol.

Figure 8 .
Figure 8.The measured frequency spectrum for the AD844-based voltage-mode UAF at V o1 IBP filter, where # is the reference symbol.

Figure 9 .
Figure 9. Simulation results for the AD844-based voltage-mode UAF at Vo1 IBP filter.

Figure 10 .
Figure 10.Simulation results for the AD844-based voltage-mode UAF at Vo2 NLP filter.

Figure 9 .
Figure 9. Simulation results for the AD844-based voltage-mode UAF at V o1 IBP filter.

Figure 9 .
Figure 9. Simulation results for the AD844-based voltage-mode UAF at Vo1 IBP filter.

Figure 10 .
Figure 10.Simulation results for the AD844-based voltage-mode UAF at Vo2 NLP filter.

Figure 10 .
Figure 10.Simulation results for the AD844-based voltage-mode UAF at V o2 NLP filter.Sensors 2023, 23, x FOR PEER REVIEW 16 of 30

Figure 11 .
Figure 11.Simulation results for the AD844-based voltage-mode UAF at Vo3 NHP filter.

Figure 12 .
Figure 12.Simulation results for the AD844-based voltage-mode UAF at Vo4 BR filter.

Figure 12 .
Figure 12.Simulation results for the AD844-based voltage-mode UAF at V o4 BR filter.Sensors 2023, 23, x FOR PEER REVIEW 17 of 30

Figure 13 .
Figure 13.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at Vo1 IBP filter.

Figure 14 .
Figure 14.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at Vo2 NLP filter.

Figure 13 .
Figure 13.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at V o1 IBP filter.

Figure 13 .
Figure 13.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at Vo1 IBP filter.

Figure 14 .
Figure 14.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at Vo2 NLP filter.

Figure 14 .
Figure 14.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at V o2 NLP filter.

Figure 14 .
Figure 14.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at Vo2 NLP filter.

Figure 15 .
Figure 15.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at Vo3 NHP filter.

Figure 15 .
Figure 15.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at V o3 NHP filter.Sensors 2023, 23, x FOR PEER REVIEW 18 of 30

Figure 16 .
Figure 16.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at Vo4 BR filter.

Figure 17 .
Figure 17.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at Vo1 IBP filter.

Figure 16 .
Figure 16.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at V o4 BR filter.

Figure 16 .
Figure 16.Gain (top) and phase (bottom) measurement results for the AD844-based voltage-mode UAF at Vo4 BR filter.

Figure 17 .
Figure 17.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at Vo1 IBP filter.

Figure 17 .
Figure 17.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at V o1 IBP filter.

Figure 18 .
Figure 18.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at Vo2 NLP filter.

Figure 19 .
Figure 19.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at Vo3 NHP filter.

Figure 18 .
Figure 18.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at V o2 NLP filter.

Figure 18 .
Figure 18.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at Vo2 NLP filter.

Figure 19 .
Figure 19.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at Vo3 NHP filter.

Figure 19 .
Figure 19.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at V o3 NHP filter.Sensors 2023, 23, x FOR PEER REVIEW 20 of 30

Figure 20 .
Figure 20.Ideal, simulated, and measured results for the AD844-based voltage-mode UAF at V o4 BR filter.

Figure 21 .
Figure 21.The simulated quality factor for the AD844-based voltage-mode UAF.

Figure 22 .
Figure 22.The measured quality factor for the AD844-based voltage-mode UAF.

Figure 22 .
Figure 22.The measured quality factor for the AD844-based voltage-mode UAF.

Figure 22 .
Figure 22.The measured quality factor for the AD844-based voltage-mode UAF.

Figure 23 .
Figure 23.Ideal, simulated, and measured results for independent quality factor control.

Figure 24 .
Figure 24.The simulated resonant frequency for the AD844-based voltage-mode UAF without affecting the parameter Q.

Figure 23 .Figure 23 .
Figure 23.Ideal, simulated, and measured results for independent quality factor control.

Figure 24 .
Figure 24.The simulated resonant frequency for the AD844-based voltage-mode UAF without affecting the parameter Q.

Figure 24 . 30 Figure 25 .Figure 25 .
Figure 24.The simulated resonant frequency for the AD844-based voltage-mode UAF without affecting the parameter Q. Sensors 2023, 23, x FOR PEER REVIEW 23 of 30

Figure 25 .
Figure 25.The measured resonant frequency for the AD844-based voltage-mode UAF without affecting the parameter Q.

Figure 26 .
Figure 26.Ideal, simulated, and measured results for independent resonant frequency control without affecting the parameter Q.

Figure 26 .
Figure 26.Ideal, simulated, and measured results for independent resonant frequency control without affecting the parameter Q.

3. 2 .
The On-Chip CMOS VM-UAF Simulation and Measurement Results Passive components of the on-chip CMOS CFOA-based voltage-mode UAF are designed as C 1 = C 2 = 15 pF and R i = 20 kΩ (i = 1 to 6) with a resonance frequency of f o = 530.5 kHz. Figure 27 shows the overall layout of the CFOA-based voltage-mode UAF and its chip micrograph with two CFOA-based voltage-mode UAFs.The CMOS implementation of CFOA is shown in Figure 28 [40].In Figure 28, the length (L) and width (W) of transistors M1 to M16 are 0.4 µm and 75 µm, the L and W of transistors M17 to M20 are 0.8 µm and 13 µm, and the L and W of transistors M21 to M28 are 0.4 µm and 26 µm.
also show the measurements for the CFOA-based voltage-mode UAF chip.The experimental and simulation results of the CFOA-based voltage-mode UAF chip relative to the theoretical analysis are shown in Figures 34-36, respectively.Sensors 2023, 23, x FOR PEER REVIEW 24 of 30 measured spurious-free dynamic range is 43.55 dBc.Figures 31-33 also show the measurements for the CFOA-based voltage-mode UAF chip.The experimental and simulation results of the CFOA-based voltage-mode UAF chip relative to the theoretical analysis are shown in Figures 34-36, respectively.

Figure 27 .Figure 27 .
Figure 27.The overall layout of the CFOA-based voltage-mode UAF and its micrograph of a chip with two CFOA-based voltage-mode UAFs.V DD

Figure 27 .Figure 28 .
Figure 27.The overall layout of the CFOA-based voltage-mode UAF and its micrograph of a chip with two CFOA-based voltage-mode UAFs.V DD

Figure 30 .
Figure 30.The measured frequency spectrum for the CFOA-based voltage-mode UAF chip at Vo1 IBP filter, where # is the reference symbol.

Figure 30 .
Figure 30.The measured frequency spectrum for the CFOA-based voltage-mode UAF chip at Vo1 IBP filter, where # is the reference symbol.

Figure 30 .
Figure 30.The measured frequency spectrum for the CFOA-based voltage-mode UAF chip at V o1 IBP filter, where # is the reference symbol.

Figure 31 .
Figure 31.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo1 IBP filter.

Figure 32 .
Figure 32.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo2 NLP filter.

Figure 33 .
Figure 33.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo3 NHP filter.

Figure 31 .
Figure 31.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at V o1 IBP filter.

Figure 31 .
Figure 31.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo1 IBP filter.

Figure 32 .
Figure 32.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo2 NLP filter.

Figure 33 .
Figure 33.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo3 NHP filter.

Figure 32 .
Figure 32.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at V o2 NLP filter.

Figure 31 .
Figure 31.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo1 IBP filter.

Figure 32 .
Figure 32.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo2 NLP filter.

Figure 33 .
Figure 33.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at Vo3 NHP filter.

Figure 33 .
Figure 33.Gain (top) and phase (bottom) simulation results for the CFOA-based voltage-mode UAF chip at V o3 NHP filter.

Figure 34 .
Figure 34.Ideal, simulated, and measured results for the CFOA-based voltage-mode UAF chip at Vo1 IBP filter.

Figure 35 .
Figure 35.Ideal, simulated, and measured results for the CFOA-based voltage-mode UAF chip at Vo2 NLP filter.

Figure 34 .
Figure 34.Ideal, simulated, and measured results for the CFOA-based voltage-mode UAF chip at V o1 IBP filter.

Figure 34 .
Figure 34.Ideal, simulated, and measured results for the CFOA-based voltage-mode UAF chip at Vo1 IBP filter.

Figure 35 .
Figure 35.Ideal, simulated, and measured results for the CFOA-based voltage-mode UAF chip at Vo2 NLP filter.

Figure 35 .
Figure 35.Ideal, simulated, and measured results for the CFOA-based voltage-mode UAF chip at V o2 NLP filter.Sensors 2023, 23, x FOR PEER REVIEW 28 of 30

Figure 36 .
Figure 36.Ideal, simulated, and measured results for the CFOA-based voltage-mode UAF chip at Vo3 NHP filter.

Figure 36 .
Figure 36.Ideal, simulated, and measured results for the CFOA-based voltage-mode UAF chip at V o3 NHP filter.

Table 1 .
Comparison of the proposed CFOA-based voltage-mode UAF with previously published filters.