International Journal of Affective Engineering Vol.13 No.4 (Special Issue) pp.245-251 (2014) ... 3,. IC does not flow because PD is connected in the reverse direction against voltage source .... Classic: W.A. Mozart, Symphony No.35 in D major,.
International Journal of Affective Engineering Vol.13 No.4 (Special Issue) pp.245-251 (2014)
Special Issue on 2013 ICBAKE (International Conference on Biometrics and Kansei Engineering), Part1
ORIGINAL ARTICLE
Novel Audio Amplifier and its Kansei Evaluation Junichi FUJITA, Yusuke KAWAKAMI, Katsushi TAKAHASHI, Kensho OKAMOTO and Tetsuo HATTORI Graduate School of Engineering, Kagawa University, 2217-20 Hayashi-cho, Takamatsu-shi, Kagawa 761-0396, Japan Abstract: This paper presents a completely new and simple audio amplifier system using the opto-coupling of LED (Light Emitting Diode) and PD (Photo Diode), without using conventional devices such as Transistor, IC and Vacuum Tube. This paper also describes the reason why the opt-coupling device works in the same way as a bipolar junction transistor and explains why the audio amplifier can be realized in a very simple form. Since we have felt that the presented audio amplifier shows good sound with very low noise, we have evaluated the characteristics of sound signal from the audio amplifier. As for the Kansei evaluation, we have obtained the experimental result that it varies depending on the type of songs (music). NAA is inferior CAA (Conventional Audio Amplifier) in some items. However, it was found to be comparable to the overall. Keywords: audio amplifier, LED and PD, opto-coupling, music sound, Kansei evaluation, questionnaire
1. INTRODUCTION
2. NOVEL AMPLIFIER
It is well known that the bipolar transistor is a semiconductor device capable of amplifying a small electric signal to a significant output level, e.g. of volt-order, in the case of analogue application. We noticed that the amplifier, such as a transistor can be realized by combining the light emitting diode (LED) and photodiode (PD) or silicon solar cell, with the positive feedback manner [1]. The first prototype of the device was made in 2010. However, first prototype amplifier was able to only voltage amplification. Power amplification has become possible by the subsequent improvement. Presently, we are performing research on the advanced circuit, e.g. operational amplifier using the entirely new device based on our study on the behavior of the device [2-4]. According to our literature search, there are only two similar researches in the world other than us [5, 6]. And, Refs. [7] and [8] are the literatures related to the Ref. [6]. However, no practical devices were developed in their works. This paper presents our new amplifying device that consists of LED and PD, and novel audio amplifier (NAA) using this new amplifying device. And also, in order to evaluate the NAA and to compare with the conventional audio amplifier (CAA), we show not only the electrical characteristics but also the Kansei (feeling) evaluation results of both NAA and CAA.
2.1 Structure Figure 1 shows the circuit connection and the picture of the new amplifier. The amplifier consists of four IR-LEDs, which are connected in series and a Si-PD. Forward voltage of each IR-LED is VF = 1.3 to 1.5 V. Therefore, collector current IC of the amplifier flows from the vicinity of VCE = 3 to 4 V. Figure 2 (a) shows the schematic of the new amplifier. It is configured in the same manner as a typical transistor circuit. Figure 2 (b) shows the amplification waveform
(a) Opto-coupling in the new amplifier (b) Picture of new device
Figure 1: Structure of the new amplifier.
(a) Schematic of new amplifier.
(b) Amplification waveform.
Figure 2: New amplifier and its amplification waveform.
Received 2014.03.13 Accepted 2014.11.10
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International Journal of Affective Engineering Vol.13 No.4 (Special Issue)
The factor α is defined as the ratio of the current flowing through the PD and the current flowing through the LED as shown in Eq. (3).
using the new ampifier. We can obtain a voltage gain more than 40dB by adjusting each value of RC, RB and V2 in Fig. 2 (a). During an experiment, new amplifier suddenly turned as if a thyristor when the input current to LED exceeded a certain value. The cause of the incident was the superposition of ambient room light onto the silicon photodiode. Through such a happening as a background, we started to investigate the phenomena caused by LED and PD in detail. And it was found that the thyristor mode occurred under a special condition. That is, collector current IC enhances very large. We call this state “thyristor mode”.
Therefore, IC is expressed as Eq. (4).
(4)
At this time, Eq. (4) can be expressed as Eq. (5). Because, IE = IB as shown in Eq. (2). (5) At the second stage, IC adds to IB , so resultant IE becomes IE = IB + IC = IB + α IB . And, at the third stage, IC increased as Eq. (6). Therefore the light intensity of the LED also increases.
2.2 Principle of Amplification In this section, we explain about the amplification principle of the new amplifier [9]. In the circuit of Fig. 3, IC does not flow because PD is connected in the reverse direction against voltage source V. Therefore,
(when IB = 0) (1)
(6)
Each value of IE and IC are enhanced in a chain reacting manner and finally IC becomes as follows
As shown in Fig. 4, base-current IB flows through the LED connected between base and emitter when the switch SW2 is turned on. Hence, (when IB flows)
(3)
(7) (8)
(2)
In Eq. (8), (α + α 2 + α 3 + …) is the well-known the infinite progression and it sum will be expressed as Eq. (9) when α is 0 ≤ α < 1,
Then, the LED emits light and the LED light is incident on the PD, because the LED and the PD is optically faced each other. Consequently, photovoltaic effect occurs in PD and the photocurrent IC generates and flows through RC and the PD.
(9) IC becomes as follows.
(10)
The ratio of IC and IB that denotes β is shown in Eq. (11). (11) In Eq. (11), if α = 0.5, then β = 0.5. If α = 0.9, then β = 9. As α exceeds 0.9, β becomes great value, e.g. in the case when α = 0.99, β = 99. On the other hand, in the case when, IC diverges to infinity namely.
Figure 3: schematic of NAA (SW2 is off).
(12)
That is, IC enhances very large. We call this state “thyristor mode”. The relationship between IE and the operating mode, namely, whether α
