Minority carrier strage device for scanners

Abstract

A novel scanning device utilizing the mino rity carrier storaee effect in a bipolar transis tor ( MCSD ) is presented. MCSD principle opera tion and imaging application are mentioned. MCSD has a working frequency range that depends on the characteristics of the transistors in use, that is, 0.6 -1014Hz ( life time TF= 50 nsec ) or 0. 1 -0.5 MHz ('tF=600 nsec). The computed working range also shows the essential influence of the time constants of transistors. An integra ted MCSD with 64 stages and 64 photo-transistors is discussed. EiTRODUCTION The scanner is important for devices sequen tially driving photo-sensing elements, light-emi tting diodes and so on. Conventional scanners, composed of more than 4 components, are limited by the decrease in the packing density of these devices(l). Bucket-brigade scanners are limited in the number of integrated stages because of their transfer inefficiency(2). To overcome this problem, it is necessary to reduce the number of components of each stage of the scanner without transfer inefficiency. MCSD comprises only one transistor or two per one stage, and has no transfer inefficiency. In this paper, basic MCSD operation and results and diffi culty in imaging application are reported. BASIC OPERATION Principle of operation Figure 1 shows measurements of the minority carrier storage effect in a bipolar transistor. This is the collector current response when bias is applied between the collector and emitter with the base floated after the collector junction was forward biased. It is observed that the response time Ts is almost constant,even if the recovering collector current (Ir) is varied to be larger than the forward collector current(If). Response time Ts is given by Eq.(l). Ts 'CF 1 1 If 1 _ o.N 0.1 In( 1 + 1 -o.N Ir ( 1) 63 where <F is the life time measured by Kuno's way( 3) and where o.N and 0.1 are the normal and inverse current amplification factor with the base groun ded, respectively. Time Ts can be regarded as the holding time of the temporary memory of the minority carrier storaging. Equation(l) suggests that the minority carrier storage effect in a bipolar transistor may be a temporary memory with a holding time of the order of life time'tF and with no inefficiency in transfer of the informa tion ( i.e. If=Ir ) . Basic circuit and operation l"igure 2 shows the basic MCSD circuit. Each stage of the basic MCSD is composed of a transi stor. Each MCSD transistor belongs to one of two groups, common with the collector. The MCSD operates as follows. Two-phase-clock voltage sou rces, Vc and Vc, are varied periodically between o and Vh (Vh::ol-3 volts). If there is no input signal, each transistor admits no current flow, except for transient leakage current induced with the Vc and Yc. If there is an input signal on the Vi terminal, the collector junction of the first Tl admits forward current flow, allows minority carrier injection and its storage, at Vc=O and Vc=Vh. In the next period, at Vc=Vh and Vc = 0, the first Tl allows current flow from collector to emitter, contro...