Synchronous semiconductor memory device having stable data output timing
In a delay adjusting unit arranged in a clock delay adjusting circuit, when a drive power switch signal is at an “H” level, a transfer gate is closed, and an input signal is delayed by a delay amount of the delay unit. When drive power switch signal is at the “L” level, the transfer gate is closed, and the input signal is output without being delayed. When the current drive power of an output buffer is low, the drive power switch signal at the “L” level decreases the delay amount of an output clock signal. When the current drive power is high, the drive power switch signal at the “H” level increases the delay amount of the output clock signal.
1. A semiconductor memory device for performing input/output of data in synchronization with an external clock signal, comprising:
a memory cell array having a plurality of memory cells arranged in rows and columns;
a clock generating circuit generating an internal clock signal by delaying said external clock signal by a predetermined delay amount; and
a data output circuit providing a data signal read from said memory cell array to an output node in synchronization with said internal clock signal, wherein
said data output circuit includes:
a plurality of first current drive portions coupled in parallel between a voltage corresponding to a first level and said output node, and each having a control node,
a plurality of second current drive portions coupled in parallel between a voltage corresponding to a second level and said output node, and each having a control node, and
means for producing a drive power switch signal controlling a current drive power applied to the output node at an intended level,
each of said plurality of first current drive portions forms a current path between the voltage corresponding to said first level and said output node in accordance with said drive power switch signal received on the corresponding control node,
each of said plurality of second current drive portions forms a current path between the voltage corresponding to said second level and said output node in accordance with said drive power switch signal received on the corresponding control node, and
said clock generating circuit includes:
a delay circuit producing said internal clock signal by delaying said external clock signal by said predetermined delay amount, and
a delay adjusting circuit determining the delay amount of said delay circuit in accordance with said drive power switch signal.
2. The semiconductor memory device according to claim 1 , wherein
said delay adjusting circuit increases the delay amount of said delay circuit in accordance with said drive power switch signal instructing increase in current drive power applied to said output node, and decreases the delay amount of said delay circuit in accordance with said drive power switch signal instructing decrease in current drive power applied to said output node.
3. The semiconductor memory device according to claim 2 , wherein
said delay circuit includes a plurality of delay units each delaying said external clock signal by a unit delay amount in accordance with the corresponding drive power switch signal.
4. The semiconductor memory device according to claim 3 , wherein
said clock generating circuit further includes:
a selecting portion for nonvolatilely setting said drive power switch signal to one of valid and invalid states, and
said delay adjusting circuit is disabled not to control the delay amount of said delay circuit when said selecting portion sets said drive power switch signal to the invalid state, and is enabled to control the delay amount of said delay circuit when said selecting portion sets said drive power switch signal to the valid state.
5. The semiconductor memory device according to claim 4 , wherein
said select portion has a program portion nonvolatilely changing from a first state to a second state in accordance with external program input, and
an activation signal for setting said drive power switch signal to the valid or invalid state is produced in accordance with a state of said program portion.
6. The semiconductor memory device according to claim 4 , wherein
said select portion has a mode register storing a plurality of setting parameters being externally set and corresponding to a plurality of operation modes in the semiconductor memory device, respectively, and
an activation signal for setting said drive power switch signal to the valid or invalid state is produced in accordance with the setting parameter stored in said mode register.