1. Field of the Invention
This invention relates to a charge coupled device, and more particularly to an output detector thereof for converting a quantity of charges transferred along a channel in the charge coupled device.
2. Description of the Prior Art
The charge coupled device in the prior art is formed on a silicon substrate. A channel region on the substrate is surrounded by a high impurity concentration field region. A plurality of gate electrodes are formed on the channel region via an insulating film to transfer charges along the channel region in response to an application of clock pulses to the gates. At the end of the series of the gates, a different conductivity region is formed to change a quantity of transferred charges into a voltage potential. The obtained voltage potential is too low to treat as an electrical signal. Therefore, the obtained voltage is applied to a gate electrode of an MOS field effect transistor formed on another part of the silicon substrate. The amplified voltage by the MOS field effect transistor is used as an electrical signal for further processing.
The different conductivity region is formed across the channel region and contacts the high impurity concentration field region. This contact and the contact with the substrate accompany a large capacitance to the different conductivity region. Here, the quantity of received charges is changed into a voltage value in accordance with an equation of Q=C.multidot.V where Q, C and V are respectively quantity of charges, capacitance and voltage. Thus, due to the large capacitance, the different conductivity region converts the quantity of charges to a small voltage.