JP5793229B2 - Semiconductor integrated circuit - Google Patents

Description

  The present invention relates to a semiconductor integrated circuit, and more particularly to power supply noise reduction.

  In a semiconductor integrated circuit, there is a problem that power supply noise occurs on each signal line used for data transfer between the data transmission circuit and the data reception circuit, and data transfer between the two circuits is not performed correctly.

  For this reason, measures are taken to reduce power supply noise such as ODT (On Die Termination) on a signal line used by the data receiving circuit to receive data (Non-patent Document 1).

JEDEC STANDARD, DDR2 SDRAM SPECIFICATION JESD79-2E (Revision of JESD79-2D), April 2008, JEDEC SOLID STATE TECHNOLOGY ASSOCIATION

  In the prior art, a measure for reducing the power supply noise received by the data receiving circuit, such as the ODT function, is taken, but a measure for reducing the power supply noise received by the data transmitting circuit is not taken. Usually, the data transmission circuit has a data output circuit such as a three-state buffer for data transmission. The data transmission circuit controls whether or not the data output circuit outputs transmission data based on the control signal. That is, the data transmission circuit controls whether the data output circuit outputs transmission data or sets the output to a high impedance state (HiZ).

  However, when the data transmission circuit sets the output of the data output circuit to HiZ, the power supply voltage is suddenly stopped on the signal line to which the power supply voltage has been supplied so far, so that power supply noise occurs. If the data transmission circuit switches the output of the data output circuit from HiZ to the data transmission state in order to transmit further data before the power supply noise converges, the other data is affected by the power supply noise. . Therefore, the conventional technique has a problem that data cannot be transmitted with high accuracy.

  A semiconductor integrated circuit according to the present invention includes a data transmission circuit and a data reception circuit that receives data transmitted from the data transmission circuit. The data transmission circuit outputs the data or outputs a high level. In the data output circuit that switches between the impedance state and the data output circuit, the data output circuit outputs the data at the time of data transmission, and transmits another data after the data transmission. A control circuit that outputs a control signal to the data output circuit so as to continue outputting the data that was last output during the previous data transmission.

  With the circuit configuration as described above, power supply noise can be reduced, so that data can be transmitted with high accuracy.

  According to the present invention, a semiconductor integrated circuit capable of accurately transmitting data can be provided.

1 is a diagram showing a semiconductor integrated circuit according to a first exemplary embodiment of the present invention. 1 is a diagram showing a semiconductor integrated circuit according to a first exemplary embodiment of the present invention. 3 is a timing chart showing an operation of the semiconductor integrated circuit according to the first exemplary embodiment of the present invention.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. For clarity of explanation, duplicate explanation is omitted as necessary.

Embodiment 1
Embodiment 1 of the present invention will be described with reference to the drawings. The present invention is applicable to a circuit that includes a data transmission circuit and a data reception circuit that receives data from the data transmission circuit, and in which data transmission from the data transmission circuit is controlled by a control signal. . In this embodiment, a signal line (hereinafter simply referred to as a bidirectional signal line) that includes a SoC (System On Chip) circuit and an SDRAM (Synchronous Dynamic Access Memory) circuit, and performs bidirectional data transfer between the two circuits. An example will be described in which data transfer is performed via the network.

  FIG. 1 is a semiconductor integrated circuit according to a first embodiment of the present invention. The circuit shown in FIG. 1 includes an SoC circuit (data transmission circuit) 100 and an SDRAM circuit (data reception circuit) 101. Data transfer between these two circuits is performed according to the DDR (Double data rate) standard.

  First, the circuit configuration of the first embodiment will be described. The SoC circuit 100 outputs a 2-bit width clock CK and a 2-bit width clock CKB, which is a differential signal of the clock CK, to the SDRAM circuit 101. The SoC circuit 100 outputs a 16-bit width control signal CMD including a command for each address of the SDRAM circuit 101 to the SDRAM circuit 101. The SDRAM circuit 101 takes in the control signal CMD in synchronization with the clocks CK / CKB.

  Further, between the SoC circuit 100 and the SDRAM circuit 101, the 32-bit width data DQ, the 4-bit width strobe signal DQS, and the differential signal DQSB thereof are transmitted and received bidirectionally. The reception side circuit serving as the data reception side takes in the reception data DQ in synchronization with the strobe signals DQS / DQSB. For the sake of convenience, the above signal names also represent signal line names at the same time.

  FIG. 2 is a diagram illustrating one-bit bidirectional signal lines (strobe signal lines DQS [3: 0] / DQSB [3: 0] and data signal lines DQ [31: 0]) in the circuit of FIG. Only a 1-bit signal line) and corresponding peripheral circuits are shown. Here, a case where the one-bit bidirectional signal line is the data signal line DQ [0] will be described as an example. The data signal line DQ [0] is connected between the SoC circuit 100 and the SDRAM 101 as described above.

  The SoC circuit 100 outputs a control signal to the external terminal 201, the buffer 202, a data output circuit 203 that outputs transmission data, a termination circuit 204 having an ODT function, and the data output circuit 203 and the termination circuit 204. A control circuit 205 and an inverter 206 are provided. The termination circuit 204 includes resistors 207 and 208 and switches 209 and 210. The data output circuit 203 includes a NAND circuit 251, a NOR circuit 252, and transistors 253 and 254. The case where the switch 209 and the transistor 253 are P-channel MOS transistors and the switch 210 and the transistor 254 are N-channel MOS transistors will be described as an example.

  In the SoC circuit 100, the data signal line DQ [0] is connected to the input terminal of the buffer 202 and the output terminal of the data output circuit 203 via the external terminal 201.

  A termination circuit 204 is provided between the external terminal 201 and the buffer 202. In the termination circuit 204, a switch 209 and a resistor 207 are connected in series between the high potential side power supply terminal VDD and the node N1 on the signal line connecting the external terminal 201 and the buffer 202. A switch 210 and a resistor 208 are connected in series between the low potential side power supply terminal VSS and the node N1. More specifically, the source terminal of the switch 209 is connected to the high potential side power supply terminal VDD. The drain terminal of the switch 209 is connected to one end of the resistor 207. The other end of the resistor 207 is connected to one end of the resistor 208. The other end of the resistor 208 is connected to the drain terminal of the switch 210. The source terminal of the switch 210 is connected to the low potential side power supply terminal VSS. The other end of the resistor 207 and one end of the resistor 208 are commonly connected to the node N1. Note that the switch 209 and the resistor 207 connected in series between the high-potential-side power supply terminal VDD and the node N1 may be switched in connection. Similarly, the switch 210 and the resistor 208 connected in series between the low-potential-side power supply terminal VSS and the node N1 may be interchanged.

  An output terminal of the buffer 202 is connected to an input terminal IN for data input of the control circuit 205. The output terminal C1 of the control circuit 205 is connected to the gate terminal of the switch 209 and is connected to the gate terminal of the switch 210 via the inverter 206. Such a configuration of the peripheral circuit is also adopted for other bidirectional signal lines. Note that the control circuit 205 is provided in common for each bidirectional signal line.

  The output terminal OUT for data output of the control circuit 205 is connected to one input terminal of the NAND circuit 251 of the data output circuit 203 and one input terminal of the NOR circuit 252. The output terminal E1 for outputting the control signal 230 of the control circuit 205 is connected to the other input terminal of the NAND circuit 251 of the data output circuit 203 and is connected to the other input terminal of the NOR circuit 252 via the inverter 255. The The output terminal of the NAND circuit 251 is connected to the gate terminal of the transistor 253. The output terminal of the AND circuit 252 is connected to the gate terminal of the transistor 254. The transistors 253 and 254 are connected in series between the high potential side power supply terminal VDD and the low potential side power supply terminal VSS. That is, the transistors 253 and 254 constitute an inverter. The drain terminal of the transistor 253 and the drain terminal of the transistor 254 are commonly connected to a node on the signal line between the buffer 202 and the external terminal 201.

  Next, the operation of the first embodiment will be described. A case where the SoC circuit 100 receives (reads) data from the SDRAM circuit 101 will be described. First, the SoC circuit 100 outputs a control signal CMD to the SDRAM circuit 101. Thereafter, the SDRAM circuit 101 transmits, for example, the data DQ at the address specified by the control signal CMD and the strobe signals DQS / DQSB to the SoC circuit 100. At this time, the data DQ transmitted from the SDRAM circuit 101 has a predetermined burst length.

  The SoC circuit 100 receives each signal via the corresponding signal line, the external terminal 201, and the buffer 202. The SoC circuit 100 receives the data DQ in synchronization with the strobe signals DQS / DQSB. Data received by the SoC circuit 100 is input to the control circuit 205 and other peripheral circuits (not shown). A period from when the SoC circuit 100 transmits the control signal CMD to when reception of the data DQ is started is referred to as read latency (RL).

  The SoC circuit 100 turns on the ODT function of the corresponding termination circuit 204 in order to suppress power supply noise generated on the data signal line DQ and the strobe signal line DQS / DQSB when receiving data from the SDRAM circuit 101. . That is, the SoC circuit 100 turns on the switches 209 and 210 included in each termination circuit 204 based on the control signal 200 from the control circuit 205. Then, the SoC circuit 100 sets the node on the corresponding signal line to a predetermined potential (for example, a potential that is ½ of the high potential side power supply VDD). As a result, the SoC circuit 100 can reduce power supply noise included in the received data, and can accurately receive the data.

  Further, the SoC circuit 100 controls the data output circuit 203 not to output transmission data to the SDRAM circuit 101 based on the control signal 230 from the control circuit 205. That is, the SoC circuit 100 sets the output of the data output circuit 203 to the high impedance state (HiZ) by the L level control signal 230. Here, when the control signal 230 is at the L level, the transistors 253 and 254 are all controlled to be off, so that the output of the data output circuit 203 indicates HiZ. As a result, the SoC circuit 100 can accurately receive the data transmitted from the SDRAM circuit 101 without being affected by the data output from the data output circuit 203.

  A case where the SoC circuit 100 transmits (writes) data to the SDRAM circuit 101 will be described. First, the SoC circuit 100 outputs a control signal CMD to the SDRAM circuit 101. Thereafter, the SoC circuit 100 transmits the data DQ and the strobe signals DQS / DQSB to the SDRAM circuit 101. At this time, the data DQ transmitted from the SoC circuit 100 has a predetermined burst length.

  The SDRAM circuit 101 receives the data DQ in synchronization with the strobe signal DQS / DQSB. The data DQ is written, for example, at an address specified by the control signal CMD. A period from when the SoC circuit 100 transmits the control signal CMD to when transmission of the data DQ is started is referred to as write latency (WL).

  The SoC circuit 100 turns off the ODT function of the corresponding termination circuit 204 when transmitting data to the SDRAM circuit 101. That is, the SoC circuit 100 turns off the switches 209 and 210 included in each termination circuit 204 based on the control signal 200 from the control circuit 205, and the SDRAM circuit 101 is connected to the SDRAM circuit 101 via the data output circuit 203 and the external terminal 201. Do not attenuate the potential of the data to be transmitted. As a result, the SoC circuit 100 can accurately transmit data to the SDRAM circuit 101.

  The SoC circuit 100 controls the data output circuit 203 to output transmission data to the SDRAM circuit 101 based on the control signal 230 from the control circuit 205. That is, the SoC circuit 100 controls the data output circuit 203 to output the transmission data by the control signal 230 of the H level. Here, when the control signal 230 is at the H level, the transistors 253 and 254 are controlled to be turned on / off according to the transmission data output from the control circuit 205. Thereby, the SoC circuit 100 transmits data to the SDRAM circuit 101.

  Thus, the SoC circuit 100 switches between the read mode in which the SoC circuit 100 receives data from the SDRAM circuit 101 and the write mode in which the SoC circuit 100 transmits data to the SDRAM circuit 101 by the control signal CMD. The SoC circuit 100 outputs a control signal CMD having a data length corresponding to one clock CK cycle at a predetermined interval.

  For example, the SoC circuit 100 receives / transmits data in the read / write mode, and then transmits / receives another data again in the same mode at a predetermined interval. Alternatively, the SoC circuit 100 receives / transmits data in the read / write mode, and thereafter transmits / receives another data in a mode different from the mode after a predetermined interval. Such data transmission / reception is repeated.

  Here, the present embodiment is characterized in that the SoC circuit 100 transmits data in the write mode, and then transmits another data again in the write mode at a predetermined interval. The operation at this time will be described with reference to FIG.

  First, the SoC circuit 100 outputs a control signal CMD (A in FIG. 3; hereinafter, simply referred to as “write command A”) to the SDRAM circuit 101. The SoC circuit 100 passes data DQ (D in FIG. 3) having a predetermined burst length and strobe signals DQS / DQSB corresponding thereto to the SDRAM circuit 101 through the period of the write latency WL (C in FIG. 3). Send to.

  Here, when transmitting data, the SoC circuit 100 outputs transmission data from the corresponding data output circuit 203.

  After outputting the write command A, the SoC circuit 100 outputs the write command E (E in FIG. 3) at a predetermined interval (B in FIG. 3). The SoC circuit 100 passes the data DQ (G in FIG. 3) having a predetermined burst length and the strobe signals DQS / DQSB corresponding thereto to the SDRAM circuit 101 through the period of the write latency WL (F in FIG. 3). Send to.

  At this time, the control circuit 205 transfers the data DQ based on the interval B of the write command (A, E), the write latency WL (C, F), and the burst length (D, G) of the data DQ. The period (H) that is not performed is calculated. Thereby, the control circuit 205 determines whether or not to transmit transmission data from the data output circuit 203 during a period (H) when the data DQ is not transferred. Then, the control circuit 205 outputs a control signal 230 to the data output circuit 203 based on the determination result.

  When the period (H) is less than or equal to a preset threshold value, the data output circuit 203 continues to output the last data (data 03 in FIG. 3) of the data DQ (D) during the period (H). On the other hand, when the period (H) exceeds a preset threshold value, the data output circuit 203 switches the output to HiZ during the period (H).

  If the data output circuit 203 continues to output the last output data during a period in which the data transfer is not performed (for example, H in FIG. 3) when the write mode is continuous, the output side of the data output circuit 203 No power supply noise is generated on the signal line due to the data output circuit 203 switching the output to HiZ. Therefore, the SoC circuit 100 can reduce the influence of power supply noise, which has been a problem in the related art, and can accurately transmit data.

  On the other hand, when the period in which the data transfer is not performed (for example, H in FIG. 3) exceeds the threshold value when the write mode is continuous, the data output circuit 203 outputs the output to HiZ during the period in which the data transfer is not performed. Switch to. Here, since the period during which data transfer is not performed is long, the power supply noise on the signal line that is generated when the output state of the data output circuit 203 is switched converges. Therefore, the SoC circuit 100 can output transmission data from the data output circuit 203 again without being affected by the power supply noise. That is, the SoC circuit 100 can reduce the influence of power supply noise and perform data transmission with high accuracy. The timing for switching the output of the data output circuit 203 to HiZ may be any time as long as the power supply noise converges before the next data transmission is started.

  As described above, the semiconductor integrated circuit according to the present embodiment is provided in the data transmission circuit according to the data transmission interval when the data transmission circuit (for example, the SoC circuit 100) continuously transmits data. The output of a data output circuit (for example, the data output circuit 203) is controlled. That is, it controls whether the data output circuit 203 continues to output transmission data or switches the output to HiZ according to the data transmission interval. Thereby, the semiconductor integrated circuit according to the present embodiment can reduce the influence of power supply noise and perform data transmission with high accuracy.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. In the above embodiment, the case where the SoC circuit 100 transmits data to the SDRAM circuit 101 has been described. However, the present invention is not limited to this. The present invention can also be applied when the SDRAM circuit 101 transmits data to the SoC circuit 100. In that case, it is necessary to control the data output circuit provided in the SDRAM circuit 101 as in the case of the data output circuit 203 described in the above embodiment.

  In the above embodiment, when the data transmission circuit (for example, the SoC circuit 100) continuously transmits data, the control circuit 205 performs control based on the address command interval, the write latency WL, and the burst length of the data DQ. Although the case where a signal (for example, control signal 230) is output has been described, the present invention is not limited to this. If the data output circuit 203 can be controlled based on the data transmission interval, a circuit configuration that outputs a control signal (eg, control signal 230) based on at least one of the above information (eg, address command interval) Also, it can be changed as appropriate.

  In the above embodiment, the case where the signal line on the output side of the data output circuit 203 is a bidirectional signal line has been described as an example. However, the present invention is not limited to this. The present invention is also applicable when the signal line on the output side of the data output circuit 203 is a signal line for data transmission.

  Further, the termination circuit is not limited to the circuit described in the above embodiment. A circuit configuration having a resistor and a switch connected in series between a power supply terminal having a predetermined potential (for example, a potential that is ½ of the high-potential-side power supply VDD) and a node on the corresponding signal line is also appropriate. It can be changed. Furthermore, although the case where the termination circuit is provided has been described as an example in the above embodiment, the circuit configuration can be appropriately changed to a circuit configuration that does not include the termination circuit.

  In the above embodiment, the case where the semiconductor integrated circuit includes one SDRAM circuit has been described, but the present invention is not limited to this. The semiconductor integrated circuit can be appropriately changed to a circuit configuration including a plurality of SDRAM circuits.

100 SoC circuit 101 SDRAM circuit 200 Control signal 201 External terminal 202 Buffer 203 Data output circuit 204 Termination circuit 205 Control circuit 206 Inverter 207 Resistor 208 Resistor 209 Switch 210 Switch 230 Control signal 251 NAND circuit 252 NOR circuit 253 Transistor 254 Transistor 255

Claims (7)

A first external terminal;
A second external terminal;
A transmission / reception circuit that transmits / receives data to / from the outside by the first external terminal and transmits a control signal by the second external terminal;
With
The transmission / reception circuit controls whether the data output circuit provided outside by switching the potential level of the control signal outputs the data or sets the output to a high impedance state,
The transceiver circuit to said data output circuit,
When receiving the data from the first external terminal , the control signal is set to a first potential level so as to output the data ,
When transmitting the data from the first external terminal, the control signal is set to the second potential level,
When receiving another data after receiving the data, if the data reception interval from the previous data reception to the start of another data reception is equal to or less than a threshold, the control signal is transmitted during the data reception interval. A semiconductor integrated circuit that keeps maintaining the first potential level and changes the control signal from the first potential level to the second potential level when the data reception interval exceeds the threshold.   In the case of receiving further data after data reception, the transmission / reception circuit receives the data received last at the time of the previous data reception during the data reception interval only when the data reception interval is equal to or less than a threshold value. The semiconductor integrated circuit according to claim 1, wherein the control signal is output to the data output circuit so as to continue output.   In the case where the data receiving interval exceeds the threshold when receiving another data after receiving data, the transmitting / receiving circuit sets the output of the data output circuit to a high impedance state during the data receiving interval. The semiconductor integrated circuit according to claim 2, wherein the control signal is output to the control circuit.   The data reception interval is determined based on a period from when the transmission / reception circuit outputs a data reception command to the outside until another data reception command is output. The semiconductor integrated circuit according to Item.   5. The data reception interval is determined based on a latency from when the transmission / reception circuit outputs a data reception command to the outside until data reception is started. 6. Semiconductor integrated circuit.   The semiconductor integrated circuit according to claim 1, wherein the data reception interval is determined based on a burst length of data received by the transmission / reception circuit. The data output circuit includes:
Having an inverter composed of P-channel and N-channel MOS transistors;
When the output of the data output circuit is in a high impedance state, the P-channel and N-channel MOS transistors are controlled to be turned off. When the data is output from the data output circuit, the data output circuit is controlled according to the data. The semiconductor integrated circuit according to claim 1, wherein one of the P-channel and N-channel MOS transistors is controlled to be turned on and the other is turned off.

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