Abstract:
A method for using a single pin to support both power input and power control functions for an integrated circuit, wherein the integrated circuit is in communication with a system. The method includes receiving at the pin a power input signal from the system, generating a power control signal based on the power input signal through a control signal generating circuit, and sending the power control signal to the integrated circuit.

Description:
RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/680,912, “SINGLE PIN TO SUPPORT THE MULTIPLE CONTROL FUNCTIONS, POWER INPUT AND ENABLE/DISABLE”, filed on May 13, 2005, the specification of which is hereby incorporated in its entirety by this reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to power control for electrical circuits, and more specifically to power control for electrical circuit through reduced pin count.  
         [0004]     2. Description of the Related Art  
         [0005]     A power supply voltage delivered to a circuit generally determines the standard digital threshold level of the circuit (also known as the voltage standard of the circuit), and the digital threshold level of input signals should be consistent with the digital threshold level of the circuit. When an integrated circuit (IC) is coupled to a system, it has several inputs, which may include data inputs (digital inputs) from the system, a power supply, and a power control signal from the system that enables or disables the IC. Usually, the voltage standards for the IC and for the system can be different from each other. For example, the voltage standard of the system may be 1.5V, or 1.8V, while the power supply voltage to the IC may be 3.3V or 5.0V. Consequently, the IC may not be able to receive digital inputs from the system directly because of the voltage difference. It may require a conversion to adjust the voltage of the digital inputs to meet the voltage standards of the IC.  
         [0006]     Additionally, the IC may also requires a power input signal from the system to power the digital inputs, because the power supply voltage that powers the digital inputs should be consistent with the voltage standard of the digital inputs. Therefore, the IC should have a power input pin that receives the power input signal from the system to power the digital inputs. As previously stated, the IC may also receive a power control signal from the system that instructs the IC when to power on or power down. Traditionally, an additional pin is employed by the IC to receive the power control signal. However, given the facts that the power input signal and power control signal both are generally from the same system and that it is not necessary for the IC to be powered when the system is powered off, it is desirable to have a single pin for power input and power control. As a result, the reduced pin count will advantageously reduce the power consumption and the cost. Thus, it is to such an apparatus and method that enables a single pin to support both the power input function and the power control function the present invention is primarily directed.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention advantageously provides a method and an apparatus using a single pin to support power input function and power control function for an integrated circuit. As a result, the goal of reducing the pin count and reducing the power consumption of the integrated circuit can be achieved.  
         [0008]     There is provided a method for using a single pin to support both power input and power control functions for an integrated circuit, wherein the integrated circuit is in communication with a system. The method includes receiving at the pin a power input signal from the system, generating a power control signal based on the power input signal through a control signal generating circuit, and sending the power control signal to the integrated circuit. The power control signal is used to control the power status of the integrated circuit.  
         [0009]     There is also provided an apparatus for using a single pin to support both power input and power control functions for an integrated circuit, wherein the apparatus is capable of communicating with a system and the integrated circuit. The apparatus includes a data pad in communication between the system and the integrated circuit and a control signal generating circuit coupled to the pin and the integrated circuit. The data pad is capable of receiving input signals from the system and adjusting the input signals for use by the integrated circuit. The data pad is further coupled to the pin and the data pad receives a power input signal from the system through the pin and is powered at least by the power input signal. The control signal generating circuit detects the power input signal at the pin and generates a power control signal to control the power status of the integrated circuit based on the power input signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Features and advantages of embodiments of the invention will become apparent as the following Detailed Description proceeds, and upon reference to the Drawings, where like numerals depict like elements, and in which:  
         [0011]      FIG. 1  illustrates a block diagram of a circuit using a single pin to support the power input function and the power control function; and  
         [0012]      FIG. 2  illustrates a detailed schematic of some blocks in  FIG. 1   
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 1  illustrates a block diagram of a circuit using a single pin to support the power input function and the power control function. The embodiment includes two blocks: a data pad  102  and an internal power control signal generating circuit  104 . The circuit has a pin (VDD 1  pin) receiving power input signal VDD 1  from a system  108 .  
         [0014]     The data pad  102  interfaces between an IC  106  and a system  108  and includes a first Schmitt trigger  110 , a delay module  112  coupled to the first Schmitt trigger  110 , a second Schmitt trigger  114  coupled to the delay module  112 , and an optional level shifter  116  coupled to the second Schmitt trigger  114 . The first Schmitt trigger  110  receives a power input signal VDD 1  from the system  108  and digital input signals from the system  108 . The first and the second Schmitt triggers  110 ,  114  are capable of adjusting the digital input signals generated from the system  108  for use by the IC  106 . Due to the hysteretic characteristic of Schmitt trigger, the Schmitt triggers  110 ,  114  are able to eliminate the fluctuations of the digital input signals generated from the system  108 . It is appreciated by those skilled in the art that the Schmitt triggers used herein can be of any type. The level shifter  116  receives a power supply VDD 2  from the IC  106 , a power input signal VDD 1  from the system  108 , digital inputs from the system  108 , and a power control signal generated by the power control signal generating circuit  104 . When the voltage standard of the IC  106  is incompatible with that of the system  108 , the level shifter  116  is used to scale up or scale down the voltage level of the digital inputs from the system  108  to a desired voltage level set by the IC  106 . For example, if the digital input signals whose voltage standard is consistent with VDD 1  has a voltage of 1.8 V and the power supply of the IC (VDD 2 ) is 3.3V, the level shifter  116  is required to scale up the voltage swing of the digital input signals from 1.8V to 3.3V for internal usage of the digital inputs in the IC  106 . It should be noted that level shifter may be omitted when the voltage standard of the system  108  is consistent with that of the IC  106 .  
         [0015]     The power control signal generating circuit  104  includes a power input signal detecting block  118 , a Schmitt trigger  120 , and a buffer  122 . The power control signal generating circuit  104  is capable of detecting the power input signal VDD 1  at the pin and generating a power control signal to enable or disable the IC according to the voltage level of VDD 1 . For instance, if the voltage standard of the system is 1.8V and the VDD 1  is far below 1.8V, the power control signal generating circuit  104  will generate a power down signal to power down the IC  106 . Conventionally, the power control signal is provided by the system  108  through a dedicated pin. By detecting the voltage at VDD 1  pin and generating the power control signal according to the detected VDD 1 , the present invention advantageously reduces the pin count, thereby saving the cost and reducing the power consumption of the IC since the power consumption of an IC is influenced by the number of pins that the IC have. The data pad  102  also receives the power control signal generated by the power control signal generating circuit  104  and uses the power control signal to control the data transmission. When the power control signal is LOW, the data pad stops sending data to the IC  106 . When the power control signal is HIGH, the data pad is allowed to send data to the IC  106 .  
         [0016]      FIG. 2  illustrates a detailed schematic of the level shifter  116  and the power control signal generating circuit  104 . Referring to the power input signal detecting block  118 , when VDD 1  is LOW or the system is powered off, a current source I_CUR constantly charges up the capacitor C 1 . As a result, the output Vrc of block  118  is pulled up to HIGH. The Schmitt trigger set the voltage at Vo 1  to LOW and hence the POWER_EN signal is also LOW after passing through a buffer  122 . The POWER_EN signal in this case represents a power down signal and powers down the IC. In a converse condition, when VDD 1  is asserted to a desired level, e.g., 1.8V, or the system is powered on, the transistor MN 1  is turned on and pulls down the current from the current source I_CUR as well as discharges the capacitor C 1 . As a result, the output of the Schmitt trigger Vo 1  is asserted to HIGH. Therefore, the POWER_EN signal is also HIGH after passing through a buffer  122 . The POWER_EN signal in this case represents a power on signal and powers on the IC. The buffer  122  is used to increase the driving capability of the POWER_EN signal.  
         [0017]     Referring to the level shifter  116  illustrated in  FIG. 2 , when the digital input IN is HIGH (VDD 1  e.g. 1.8V corresponding to the voltage level of the system) and the POWER_EN is also HIGH, the digital input turns on the transistor MN 1 , but turns off the transistor MN 2 , and hence turns on transistor MP 2  while turns off the transistor MP 1 . This will scale up the output voltage OUT of the level shifter  116  to HIGH (VDD 2  e.g. 3.3V). When POWER_EN is LOW, the output POWER_ENB of the inverter INV 1  is asserted to HIGH, which in turn pulls down the OUT to LOW.  
         [0018]     The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described (or portions thereof, and it is recognized that various modifications are possible within the scope of the claims. Other modifications, variations, and alternatives are also possible. Accordingly, the claims are intended to cover all such equivalents.