Read-out circuitry for an image sensor
An array of image sensing elements is arranged in rows and columns. A readout circuit for each column includes a circuit configured to receive a column select signal. A memory stores data indicative of a voltage of an image sensing element which is being read. An analog to digital conversion circuit provides an output to the memory to control the storing of data. The output is dependent on the voltage of the image sensing element. Power control circuitry operates to disable, at least partially, the analog to digital conversion circuit when the column has not been selected.
1. A circuit for read out from an image array including a plurality of column lines, said circuit comprising, for each column line:
an analog-to-digital conversion circuit having an input coupled to the column line, said analog-to-digital conversion circuit enabled for operation in response to a conversion enable signal;
a control circuit configured to generate said conversion enable signal, the control circuit comprising:
a first control circuit having a data input configured to receive a first column enable signal, an enable input configured to receive a first row style signal and a data output configured to generate a first output enable signal; and
a second control circuit having a data input configured to receive a second column enable signal, an enable input configured to receive a second row style signal and a data output configured to generate a second output enable signal;
wherein the conversion enable signal is derived from the first and second output enable signals; and
wherein the first row style signal specifies a first pattern of column lines for read from the image array and wherein the second row style signal specifies a second pattern of column lines for read for read from the image array.
2. The circuit of claim 1 , wherein the analog-to-digital conversion circuit comprises:
a sample and hold circuit having an input coupled to the column line; and
a comparator circuit having a first input coupled to an output of the sample and hold circuit and a second input coupled to receive a ramp signal;
wherein the sample and hold circuit and comparator circuit are enabled for operation in response to said conversion enable signal.
3. The circuit of claim 1 , wherein the first and second control circuits are flip-flop circuits.
4. The circuit of claim 1 , further comprising:
a column decoder configured to generate a column selection signal for each column; and
a logic gate for each column configured to logically combine the column selection signal with a write style signal to generate a write control signal applied to control a write operation by the first and second control circuits to store the first and second column enable signals, respectively.
5. The circuit of claim 1 , further comprising, for each column, a plurality of memory cells clocked by an output of the analog-to-digital conversion circuit, wherein each memory cell of the plurality of memory cells receives a different bit of coded signal.
6. The circuit of claim 5 , wherein the analog-to-digital conversion circuit, when enabled by the conversion enable signal, is configured to compare a voltage on the column line to a ramp signal, and wherein the coded signal varies corresponding to change in the ramp signal.
7. The circuit of claim 1 , further comprising a logic circuit configured to logically combine the first and second output enable signals to generate the conversion enable signal.
8. The circuit of claim 7 , wherein said logic circuit asserts the conversion enable signal only if both the first and second output enable signals are asserted.