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This paper presents a new current conveyor (CCII+) full-wave rectifier for low frequency/small signal medical applications. The proposed rectifier is based on the current conveyor full-wave rectifier proposed previously, but the proposed rectifier is better in view of no need diodes to rectify, and no need bias sources to overcome the zero crossing error. It needs only two CCII+s, two resistors, and three simple current mirrors, which is easy for IC implementation and for building in many countries. The PSPICE simulation with the current conveyor CCII+ in the current feedback opamp AD844 IC and the 2N2222 bipolar current mirror shows the good low frequency/small signal rectification, the operation voltage of down to 6 .

In the past few decades, medical and biological researches gained more and more attention. The ever-growing need for such researches caused many medical applications to develop. Collecting data from a living human body is a complex task and needs circumspection.

Low frequency full-wave rectifiers are important building blocks for small signal processing in biomedical systems. These circuits should not introduce any form of distortion that can destroy the information contained. For this reason, the analog processing blocks must present high performance over the frequency of interest.

As well-known the operation of diode-only rectifier is limited by the threshold voltage of the diode, approximately 0.3 V for the germanium diode and 0.7 V for the silicon diode. Thus, the diode-only rectifier is used in those applications in which the precision in the range of threshold voltage is insignificant. For application requiring high accuracy, the diode-only rectifiers cannot be used; integrated circuit (IC) rectifiers are used instead.

One advantage of the IC rectifier designed using the simple devices such as opamps, current conveyors (CCII), current mirrors, diodes, and resistors as components is that they can be built in many countries.

Recently, the current mode full-wave rectifier using dual CCII as the voltage to current converter has received much attention. For example, [

In this paper, the author presents a new CCII full-wave rectifier for low frequency/small signal medical applications that is better than the previous CCII full-wave rectifiers as follows.

- The proposed rectifier does not consist of the diodes as the previous rectifiers [

- The proposed rectifier does not use the bias sources to make diodes turning-on all the time to overcome the zero crossing error as the previous rectifiers [

- The proposed rectifier has the temperature stability on the zero crossing performance to be better than the previous rectifiers [

The proposed full-wave rectifier is shown in

The operation of the circuit is as follows. The second generation current conveyor CCII+ [

i Y = 0 v X = v Y i Z = i X } (1)

_{in} through R_{in}. This input current is mirrored to nodes Z of two CCIIs as the two out-of-phase currents.

i Z 1 = − i Z 2 = V i n R i n = I i n (2)

where the input voltage V_{in} is (V_{in+} − V_{in}_{−}).

When V_{in}_{+} is positive, V_{in}_{−} is negative, the node Z currents of CCII1 and CCII2 make the current mirrors [

The current at the output of CM1 (I_{in}) is the negative current (the current flows into the output of CM1).

When V_{in}_{+} is negative, V_{in−} is positive, the node Z currents of CCII1 and CCII2 make the current mirrors CM2 to operate and CM1 to not operate. The current at the output of CM2 (I_{in}) is also the negative current (the current flows into the output of CM2).

Note that, when V_{in} is positive the output current of CM1 is −I_{in} and one of CM2 is zero, and when V_{in} is negative the output current of CM2 is I_{in} and one of CM1 is zero. Both output currents of the current mirrors (CM1 and CM2) are added and mirrored by CM3 to convert the direction of currents as the output of CM3. This output current is changed to the output voltage by R_{out}. The relation between the input voltage and the output voltage of the proposed full-wave rectifier can be written as

V i n > 0 ⇒ V o u t = A V V i n V i n < 0 ⇒ V o u t = − A V V i n } (3)

Because of the two out-of-phase currents at the outputs of two CCIIs, the rectifier cores (CM1 and CM2) are driven in the push-pull mode; hence, the zero crossing error can be canceled. The proposed full-wave rectifier does not use the bias sources to make diodes turning-on all the time to overcome the zero crossing error as the previous full-wave rectifiers [

Using the small signal model of the CCII in

A V = R o u t α N α P R i n + 2 R x (4)

where α N is the current gain of the simple NPN bipolar current mirror, α P is the current gain of the simple PNP bipolar current mirror [_{x} is the internal resistance at node X of the CCII [

A comparison between the proposed CCII full-wave rectifier and the previous CCII full-wave rectifiers [

Proposed rectifier | CCII rectifiers [ | CCII rectifier [ | |
---|---|---|---|

Input impedance | R_{y} | R_{y}_{ } | R_{y}/2 |

Differential mode input | Yes | Yes | No |

Output impedance | R_{ou}_{t}//r_{o}_{ } | R_{L}//(r_{D}_{(on)} + R_{z}) | R_{L}//R_{z} |

Output voltage range | Current mirror range | CCII range-diode threshold voltage | CCII range |

Diodes | - | 4 | 2 |

Resistors | 2 | 2 | 3 |

that the proposed rectifier does not use diodes as the previous rectifiers [

Using the small signal model in

Considering the output impedance, the proposed full-wave rectifier has the low output impedance, the same as the low output impedance full-wave rectifier [

The proposed full-wave rectifier was simulated by using the PSPICE program (OrCAD Release 9.1). The AD 844 ICs from Analog Devices (commercially CCII [_{CC} = +12 V and V_{EE} = −12 V. Resistors: R_{in} = 50 ohms and R_{out} = 230 ohms were chosen. This resistance will make the gain of the proposed full-wave rectifier (4) about 1; considering the 50 ohms R_{x} of the CCII in AD844 IC and the error of current mirrors. However, in the IC process, the supply voltages for the CCII can be the lower voltage if the low voltage CCII is used.

The input sine wave signal (100 mV_{peak}) is fed to the input of the proposed CCII full-wave rectifier. The output signal is displayed in

The zero-crossing performance of the proposed CCII full-wave rectifier is magnified and shown in

cannot be seen with the X-Y scale of

Comparing the previous CCII full-wave rectifiers [

It is crystal clear that the zero-crossing temperature performance of the proposed rectifier is better than those of the previous rectifiers [

In this paper, the author has reported a new CCII full-wave rectifier for low frequency/small signal medical applications, which consists of two CCIIs, two resistors, and three simple current mirrors. The proposed CCII full-wave rectifier operates in a push-pull mode. With these, the proposed rectifier yields the advantages over the previous CCII full-wave rectifiers [

Monpapassorn, A. (2018) A New Current Conveyor Full-Wave Rectifier for Low Frequency/Small Signal Medical Applications. Circuits and Systems, 9, 58-65. https://doi.org/10.4236/cs.2018.93006