Title of Invention: Memory control chip, control method and control circuit
Abstract: 
A memory control chip, control method and control circuit. Instead of accessing a plurality of memory modules in a memory bank by referencing the same clocking signal, each memory module references a clocking signal having the same frequency but a slightly different preset phase so that the data within each memory module is accessed at a slightly different time. Ultimately, simultaneous switch output noise is greatly reduced and fewer power/ground pins are required in a package. 

Summary of Invention: 

BACKGROUND OF THE INVENTION 
&lsqb;0002&rsqb; 1. Field of Invention 
&lsqb;0003&rsqb; The present invention relates to a memory circuit. More particularly, the present invention relates to a memory control chip, control method and control circuit. 
&lsqb;0004&rsqb; 2. Description of Related Art 
&lsqb;0005&rsqb; Most personal computer (PC) systems include a host board, an interface card and some peripheral devices. The host computer board is central to the operation of the computer system. Except for a central processing unit (CPU), memory control chip and slots for accommodating interface cards, the host computer board also has a plurality of memory module slots for inserting memory modules. According to system requirements, different types of memory modules may be inserted to the host board. 
&lsqb;0006&rsqb; The most frequently used memories inside a personal computer includes synchronous dynamic random access memory (SDRAM) and double data rate dynamic random access memory (DDR SDRAM). In SDRAM, data access is triggered through the rising edge or the falling edge of a clocking signal. On the other hand, data access in DDR SDRAM is triggered through both the rising edge and the falling edge of the system clock so that DDR SDRAM has a data access rate doubles that of the SDRAM for the same clocking frequency. 
&lsqb;0007&rsqb; At present, DDR SDRAM memory modules use memory module slots that adhere to the 184-lead CDEC standard. The number of data signaling leads provided by the standard is 64-bit wide and hence matches the 64-bit wide bus in the memory control chip. Therefore, each memory module can be defined as a memory bank and a batch of data 64-bit wide can be accessed at a time. To increase memory address space and reserve space for future expansion, a host board typically has an unequal number of memory module slots for plugging memory modules. Furthermore, memory modules plugged into different memory module slots often indicate memory modules belonging to a different memory bank. 
&lsqb;0008&rsqb; FIG. 1 is a schematic block diagram of a conventional memory control circuit. The circuit in FIG. 1 includes a memory control chip 110, a clock buffer 140, a first memory module 120 and a second memory module 130. The first memory module 120 and the second memory module 130 are plugged into two memory module slots, which belong to different memory banks (not shown), so that data within the memory modules 120 and 130 can be accessed through the memory control chip 110. In FIG. 1, the number of data signaling leads (DATA) in the memory control chip 110 as well as the number of data signaling leads SD1 and SD2 in the first memory module 120 and the second memory module 130 are also 64. Hence, the memory control chip 110 is able to use a 64-bit wide data bus 115 to access data within those memory modules 120 and 130. The clock generator lead (DCLK0) in the memory control chip 110 is connected to the clock input terminal (CKI) of the clock buffer 140 for boosting the driving capacity of the clocking signal. The clock output terminal (ck01) of clock buffer 140 outputs a clocking signal to drive both the first memory module 120 and the second memory module 130 (the clock buffer 140 outputs a clocking signal capable of driving at most 4 banks of memory modules). Hence, clocking signals are transmitted to the first memory module 120 and the second memory module 130 as reference clock signals during a data access operation. The clock buffer 140 also has a clock feedback output terminal (CK02) for transmitting clocking signals back to a clock feedback input terminal (DCLKI) in the memory control chip 110. The memory control chip 110 also has a phase lock circuit (not shown) for adjusting the clocking phase of the signal transmitted from the clock signal output terminal (DCLKO). The memory modules on the memory module slots have 64-bit wide data signaling leads. Hence, when the clock generator lead (DCLKO) in the memory control chip 110 issues a clocking signal together with an address for accessing any one of the memory modules, a 64-bit data variation will appear on the data bus 115. Such variation on the data bus 115 may lead to the production of prodigious quantity of noise signals from the data signal leads (DATA) of the memory control chip, the so-called simultaneous switch output (SSO) noise. To reduce the noise, a large number of power/ground leads is set up close to the data signal leads (DATA) of the memory control chip 110. These power/ground leads increase the number of charge/discharge path when voltages at the data signal leads (DATA) vary. Consequently, the noise is controlled within an acceptable range. 
&lsqb;0009&rsqb; With recent breakthroughs in semiconductor design, computational capability of a central processing unit has multiple fold improvements. Thus, width of buses from the memory control chip of a personal computer must increase to match the speed of execution of the central processing unit. 
&lsqb;0010&rsqb; FIG. 2 is a block diagram of a conventional memory control circuit with a 128-bit wide bandwidth. The 128-bit wide data bus 155 receives signals from the memory module 162 and the memory module 164 with each memory module providing 64-bit of data signals. A host board having this type of circuit architecture requires an even number of memory modules. The circuit includes a memory control chip 150, a clock buffer 180, a third memory module 162 and a fourth memory module 164. The third memory module 162 and the fourth memory module 164 belong to the same memory bank 160 but plugged into separate memory module slots (not shown). The data signal bus leads (DATA) in the memory control chip 150 is 128-bit wide. Similarly, the sum of the number of data signal leads SD1 in the third memory module 162 and the number of data signal leads SD2 in the fourth memory module 164 is 128. Hence, the memory control chip 150 may access the data in the memory module 162 and 164 within the memory bank 160 simultaneously through the 128-bit data bus 155. The clock generator lead (DCLKO) in the memory control chip 150 is connected to the clock input terminal (CKI) of the clock buffer 180 for increasing the driving power of the clocking signal. The clock buffer 180 also has a clock output terminal (CK01) for outputting clock signals that drive both the third memory module 162 and the fourth memory module 164. Hence, clocking signals can be transmitted to the third memory module 162 and the fourth memory module 164 to serve as reference clock signals during a data access operation. The clock feedback output terminal (CK02) of the clock buffer 180 also transmits a clocking signal to the clock feedback input terminal (DCLKI) of the memory control chip 150 for adjusting the clocking phase of the signal transmitted from the clock generator lead (DCLKO). 
&lsqb;0011&rsqb; For the newer DDR SDRAM memory module having a 128-bit wide data bus, each data access operation may result in a maximum change of 128 data bits in the data bus 155. With so many bit line changes concurrently, noise created at the data signal leads (DATA) of the memory control chip 150 will be considerably more than the transition of just 64 data bits. Thus, to reduce the noise that results from accessing 128 bits of data, the number of power/ground terminals set up close to the data signal leads (DATA) must be increased. However, the memory control chip is often enclosed within a 37.5 mm by 37.5 mm package to reduce production cost. Due to a limitation in pin positions for this type of package, the number of power/ground leads is virtually fixed. Yet, without additional power/ground leads in the package, the noise problem is going to aggravate. 


SUMMARY OF THE INVENTION 
&lsqb;0012&rsqb; Accordingly, one object of the present invention is to provide a memory control chip, control method and control circuit capable of reducing noise under the constraint of having only a few power/ground leads. 
&lsqb;0013&rsqb; To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a memory control chip for accessing a plurality of memory modules within a memory bank. The memory control chip includes groups of data signal leads and a plurality of clock generator leads. Each group of data signal leads is able to connect with a group of data signal leads in one of the memory modules. The clock generator leads output corresponding clocking signals to the respective clock input lead of each memory module. All clocking signals have the same frequency but differ from each other by a preset phase. 
&lsqb;0014&rsqb; This invention also provides a memory control method for controlling a plurality of memory modules within a memory bank. First, groups of data signal leads are provided on a chip. Each group of chip data signal leads is connected to a group of data signal leads of the corresponding memory module. A plurality of clocking signals is transmitted to the clock input leads of each memory module so that each memory module may access data according to a corresponding clocking signal. All the clocking signals have the same frequency but differ from each other by a preset phase. According to the clocking signals, the chip data signal leads accesses data through the group of data signal leads of each memory module sequentially. 
&lsqb;0015&rsqb; This invention also provides a memory control circuit that includes a plurality of memory modules and a memory control chip. Each memory module has a clock input lead and a group of data signal leads. The memory modules belong to a memory bank. The memory control chip has groups of data signal leads. Each group of data signal leads is connected to a group of data signal leads in each memory module. The memory control chip also has a plurality of clock generator leads for transmitting clocking signals to the clock input lead of each memory module. All the clocking signals have identical frequency but differs from each other by a preset phase. 
&lsqb;0016&rsqb; It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.


Detailed Description: 

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
&lsqb;0022&rsqb; Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
&lsqb;0023&rsqb; FIG. 3 is a block diagram of a memory control circuit with a 128-bit data bus architecture according to one preferred embodiment of this invention. As shown in FIG. 3, the circuit includes a memory control chip 210, a clock buffer 240, a fifth memory module 222 and a sixth memory module 224. Both the fifth memory module 222 and the sixth memory module 224 belong to a memory bank 220 but plugged into separate memory module slots (not shown). 
&lsqb;0024&rsqb; The data signal leads (DATA1 and DATA2) of the memory control chip 210 are 128-bit wide. The data signal leads (SD1 and SD2) of the fifth memory module 222 and the sixth memory module 224 are 128-bit wide. So, the memory control chip 210 can use a 128-bit wide data bus to access data within the memory modules 222 and 224 of the memory bank 220. The first group of data signal leads (DATA1) is connected to a first group of data leads (SD1) of the fifth memory module 222 and data is accessed through a 64-bit wide first data bus 212. Similarly, the second group of data signal leads (DATA2) is connected to a second group of data leads (SD2) of the sixth memory module 224 and data is accessed through a 64-bit wide second data bus 214. 
&lsqb;0025&rsqb; As shown in FIG. 3, the first clock generator lead (DCLKOL) of the memory control chip 210 outputs a first clocking signal and the second clock generator lead (DCLKOH) outputs a second clocking signal. The first and the second clocking signal are transmitted to the first clock input terminal (CKI1) and the second clock input terminal (CKI2) of the clock buffer 240 for enhancing the driving capacity of the clocking signals. The first clock output terminal (CK01) and the second clock output terminal (CK02) of the clock buffer 240 output the enhanced first and second clocking signals to the clock input lead (CK1) of the fifth memory module 222 and the clock input lead (CK2) of the sixth memory module 224 respectively. Thus, the fifth memory module 222 and the sixth memory module 224 may separately reference the first clocking signal and the second clocking signal in data accessing operations. 
&lsqb;0026&rsqb; The first clock feedback output terminal (CKO11) and the second clock feedback output terminal (CKO12) of the clock buffer 240 return a first feedback clocking signal and a second feedback clocking signal to the first clock feedback input terminal (DCLKIL) and the second clod feedback input terminal (DCLKIH) of the memory control chip 210 respectively. The feedback clocking signals are references for adjusting the clocking signals output from the first clock generator lead (DCLKOL) and the second clock generator lead (DCLKOH). 
&lsqb;0027&rsqb; Because the number of power/ground leads is constrained by the 37.5 mm by 37.5 mm package in the memory control chip, the first clocking signals from the first clock generator lead (DCLKOL) and the second clocking signals from the second clock generator lead (DCLKOH) (both having an identical cycle time) are transmitted with a preset phase difference (as shown in FIG. 4, a phase difference of A exists between the clocking signals submitted by the first clock generator lead (DCLKOL) and the second clock generator lead (DCLKOH)). 
&lsqb;0028&rsqb; In other words, the fifth memory module 222 and the sixth memory module 224 reference the first clocking signal and the second clocking signal separately. Hence, the first data signals 212 and the second data signals 214 are accessed by the memory control chip 210 at different times. Since each data access operation only varies at most 64 bits of data (either the first data bus 212 or the second data bus 214 is activated), fewer power/ground leads are required and the simultaneous switch output (SSO) of the 64 bit data variation are eliminated at two different timing intervals. That means, the amount of noise due to simultaneous switch output (SSO) is greatly reduced and there is no need to add extra power/ground leads to eliminate data variation resulting from a simultaneous 128-bit variation. 
&lsqb;0029&rsqb; Obviously, the number of groups of data signal leads and the number of clock generator leads of the memory control chip 210 are not limited to two. As long as the bit width of the memory control chip is different from the conventional, the clock generator leads may be adjusted to generate clocking signals to control the data signal leads for accessing data. In the design of preset phase difference (phase A), using a DDR DRAM as an example, data access is activated through the rising and the falling edge of a clocking signal. Hence, the preset phase difference (phase A) must be controlled within half a cycle such as a quarter (¼) cycle or an eighth (&frac18;) cycle, preferably a quarter cycle. Because in a quarter cycle the first data signal 212 and the second data signal 214 has the biggest data variation interval, SSO noise can be controlled within a definite range. 
&lsqb;0030&rsqb; In addition, if the number of memory modules is few, the first clock generator lead (DCLKOL) may connect directly to the clock input lead (CK1) of the fifth memory module 222. Similarly, the second clock generator lead (DCLKOH) may connect directly to the clock input lead (CK2) of the sixth memory module 224. With this arrangement, two clocking signals having a preset phase difference also can be used to access the two memory modules within a memory bank. 
&lsqb;0031&rsqb; According to this embodiment, the first clocking signal and the second clocking signal has, for example, a frequency of 133 MHz or 166 MHz. When the first clocking signal and the second clocking signal are set to operate at 133 MHz, the data transmission rate on the first data bus 212 and the second data bus 214 is 266 MHz. If the preset phase difference is set to &frac18;th cycle of the first clocking signal, noise can be controlled within a desired range. When the first clocking signal and the second clocking signal are set to operate at 166 MHz, the data transmission rate on the first group of data signal leads (DATA1) and the data transmission rate on the second group of data signal leads (DATA2) are 333 MHz. Similarly, if the preset phase difference is set to ¼th cycle of the first clocking signal, noise can be controlled within a desired range. 
&lsqb;0032&rsqb; In conclusion, this invention provides a memory control chip, control method and control circuit that splits up data bus that references an identical clocking signal into data buses that reference clocking signals with a difference phase. In this manner, the invention has at least the following advantages: 
&lsqb;0033&rsqb; 1. The extent of simultaneous data variation is reduced and hence the magnitude of the SSO noise is lowered. 
&lsqb;0034&rsqb; 2. Fewer power/ground leads are required to combat noise and hence manufacturing cost is reduced. 
&lsqb;0035&rsqb; It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 



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