Ping-pong readout

#In an image sensor, data is produced in output. Sometimes, it is desirable to be able to do various things with the data. Sample and hold units often obtain the information, and output the information as necessary.

#It is an object of the present system to define a circuit that enables reading out pixel data at the same time as analog conversion is occurring. The present system describes the circuit which enables conserving and reading out previous conversion while doing a new conversion.

#These and other aspects of the invention will now be described with reference to the attached drawings, in which:

#FIG. 1 shows a previous system;

#FIG. 2 shows a conceptual embodiment;

#A previous system is shown in FIG. 1. A successive approximation A/D converter 100 performs a successive approximation on the information in register 102. When, but only when, that is finished, the system shifts out the information in 102 to a new register 104. It should be apparent that this system cannot carry out both at the same time.

#The present system, conceptually, uses the operation shown in FIG. 2. The successive approximation A/D converter 100 is connected to two different registers, 202 and 204. A switching unit 206 can be optionally provided to determine which of the units receives the output information. The system operates to produce its output in alternative registers during alternative clock cycles. During odd clock cycles, for example, the successive approximation A/D converter 100 operates on the information in register 202. Then, during the next even clock cycle, the successive approximation device operates on the information in register 204. During that second clock cycle, the information in 202 is completely valid. Therefore, the information can be shifted out while doing a new conversion.

#A detailed implementation is shown in FIG. 3. A plurality of bi-directional registers are used. Data is written into the registers row-wise, and readout from the register column-wise. The system is shown in FIG. 3. There are two sets of registers 300 and 302. One is always either in read-mode or write-mode, and the other is always in the opposite mode.