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IP.com Disclosure Number: IPCOM000007414D
Publication Date: 2002-Mar-22
Document File: 3 page(s) / 34K

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The IP.com Prior Art Database


An image sensor having a portrait orientation includes an array pixels having n columns and m rows. The portrait orientation includes each column having a significantly greater number of pixels than the number of pixels in each row so that, when in its normal orientation, the vertical height of the image sensor is significantly greater than the width.

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Typical image sensors found in current day electronic still and video cameras are of the so-called landscape format.  An example of this is shown below in Fig. 1.  This format is a carry over from traditional Agx film in the case of still cameras, and typical television display formats (such as NTSC) in the case of video cameras.

Fig. 1:  Landscape format image sensor with m x n pixels

For portrait photography, however, this is not necessarily the preferred format since it would require either rotating the sensor in the camera, or rotating the camera itself by 90°.  Therefore, it only seems reasonable to make a sensor in the so-called portrait format for this application, as shown in Fig. 2.

Fig. 2:  Portrait format image sensor with n x m pixels

For a given number of pixels (n x m) and optical format (APS, 35 mm, etc), it turns out that the portrait format has some advantages over the landscape format.  Firstly, the horizontal register of the portrait format sensor has fewer pixels than that of the landscape format sensor.  This results in better overall, or global, charge transfer efficiency since it is exponentially dependent on the number of transfers as given by,

Global CTE ,

where his the efficiency per transfer and NXFER is the total number of transfers in the horizontal register.  NXFER is given by nNF, where NF is the number of phases per pixel.

Secondly, for a given horizontal drive speed, it turns out that the portrait mode sensor has a slightly higher frame rate than that of the landscape sensor.  This is because the RC delay time of the vertical gate electrodes goes as the square of the width of the sensor, and this RC delay time is what limits the vertical clock pulse widths and hence, the vertical-to-horizontal transfer, or retrace time.  This can be shown as follows.

The RC time of a vertical gate electrode goes as,


where R and C are the gate electrode’s resistance and capacitance, respectively, W and L are the width and length of the gate electrode (which are both assumed to be constant, for simplicity), respectively, r is the sheet resistance of the gate electrode material in ohms/square, and eox and t ox are the permittivity and thickness of the gate electrode dielectric, respectively.  Since L is given by the number of pixels along the length of the gate electrode multiplied by the pixel size, and the vertical-to-horizontal retrace time tak...