Abstract:
A circuit monitor performance of an integrated circuit. The circuit includes a clock signal and a phase delay detection circuit. The clock signal is used by the integrated circuit to generate an output signal on an output pin of the integrated circuit. The phase delay detection circuit detects relative phase difference between the clock signal and the output signal on the output pin of the integrated circuit. The phase delay detection circuit includes a digital signal generator and an integrator. The digital signal generator is connected to an output pin of the integrated circuit. The digital signal generator generates a digital signal. Changes in phase delay between the output signal on the output pin of the integrated circuit and the clock signal used by the integrated circuit are encoded in a duty cycle of the digital signal generated by the digital signal generator. The integrator is connected to the digital signal generator and integrates the digital signal to produce an integrated signal. A voltage level of the integrated signal indicates relative phase delay between the output signal and the clock signal.

Description:
BACKGROUND 
     The present invention concerns the monitoring of the system margin of an integrated circuit. The technique presented herein may also be used to monitor the core temperature of the integrated circuit. 
     The propagation delay of signals in integrated circuits is affected by many factors. These include the voltage level of VCC, process variations in production of the integrated circuit, system variations (such as input and output capacitance to the integrated circuit) and temperature. 
     In order to assure that timing within an integrated circuit is adequate, a system margin for the integrated circuit is utilized. That is, rather than designing output signals of the integrated circuit to be available at the last possible instant, the integrated circuit is designed so that, under optimal operating conditions, the signals arrive at the destination early. This early arrival allows for delays introduced by adverse circumstances, such as a lowered VCC, an increase in temperature and unfavorable processing variations. Thus integrated circuits are generally designed to operate sufficiently even under non-optimal conditions. 
     However, the trend over time in designing integrated circuits is to continue to provide integrated circuits with lower VCC and faster operating frequency. It would be advantageous therefore for purchasers of integrated circuits to be able to measure the system margin built in by the manufacturer for the purpose of evaluation and possibly to adjust the operating parameters of the integrated circuit to, where desirable, change the system margin. 
     In addition, in many high performance integrated circuits, operation of the integrated circuit can result in the generation of a significant amount of heat. If the amount of heat is not limited or adequately dissipated, performance of the integrated circuit can be significantly impeded and/or circuitry within the integrated circuit can be destroyed. 
     In order to avoid overheating integrated circuits, the integrated circuits and the system containing the integrated circuits can be designed so that even under worst case operating conditions there will not be significant enough accumulation of heat to overheat the integrated circuit. However, this over design will result in integrated circuits which will have an overabundance of system margin and which will not perform optimally under normal operating conditions. 
     Alternatively, some way can be devised to try to determine the temperature of the integrated circuit. For instance, this could be done by measuring the temperature on the casing of the processor chip using a thermistor or similar technique. Alternatively, a software routine can be used to monitor operation of the integrated circuit, and based on past and current operations estimating the temperature of the integrated circuits. One problem with all these methods of monitoring temperature is that they are extremely inaccurate. Additionally, the added circuitry/software may be expensive to implement. 
     SUMMARY OF THE INVENTION 
     In accordance with the preferred embodiment of the present invention, a circuit is presented for monitoring performance of an integrated circuit. The circuit is useful for monitoring both system margin and core operating temperature of the integrated circuit. 
     The circuit includes a clock signal and a phase delay detection circuit. The clock signal is used by the integrated circuit to generate an output signal on an output pin of the integrated circuit. The phase delay detection circuit detects relative phase difference between the clock signal and the output signal on the output pin of the integrated circuit. 
     The phase delay detection circuit includes a digital signal generator and an integrator. The digital signal generator is connected to an output pin of the integrated circuit. The digital signal generator generates a digital signal. Changes in phase delay between the output signal on the output pin of the integrated circuit and the clock signal used by the integrated circuit are encoded in a duty cycle of the digital signal generated by the digital signal generator. 
     The integrator is connected to the digital signal generator and integrates the digital signal to produce an integrated signal. A voltage level of the integrated signal indicates relative phase delay between the output signal and the clock signal. 
     In one embodiment, the digital signal generator includes a delay flip-flop and a gate. The delay flip-flop has a D input, a clock input and a Q output, the clock signal is connected to the clock input and the output signal is connected to the D input. The gate has a signal input, a control input and an output. The output signal is connected to the signal input. The Q output is connected to the control input of the gate. The output is connected to an input of the integrator. The integrator includes a resistor and a capacitor. The resistor has a first end connected to the output of the gate. The capacitor has a first end connected to a second end of the resistor. The capacitor also has a second end connected to a reference voltage. An analog to digital converter may be connected to the first end of the capacitor. 
     In this first embodiment only the falling edge of the output signal on the output pin is utilized in deriving the voltage of the integrated signal. In a second embodiment, both the falling edge and the rising edge of the output signal on the output pin are utilized to derive the voltage on the integrated signal. This increases the number of samples of the output signal on the output pin when compared with the first embodiment. However, the second embodiment uses more components, i.e., a delay flip-flop, two NAND gates and two gates, to implement the digital signal generator. Additionally, in various embodiments, more sophisticated integrators can be used to limit noise. 
     Additionally, in one disclosed embodiment of the present invention, the phase detection circuit includes a controller which changes an operating frequency of the integrated circuit when the voltage level of the integrated signal indicates that the phase delay between the output signal and the clock signal is longer than a predetermined value. This can be used to adjust system margin “on-the-fly” so as to assurance optimal performance of the integrated circuit. 
     The present invention also allows monitoring, and thus adjustment, of operating (or system) margins within an integrated circuit through monitoring phase delay of an output signal. By observing system margin, the integrated circuit can be operated at a frequency that never violates the system timing requirements regardless of conditions. This accommodates all possible worst case conditions without sacrifice to nominal operating conditions. 
     By monitoring phase delay of integrated circuits and adjusting operating parameters in response to excessive phase delay, it is possible to operate integrated circuits at an operating frequency which is beyond the manufacturers specified maximum frequency conditions and is optimal for the particular operating conditions. 
     Further, monitoring of phase delay of output signals as taught by the present invention is useful as a manufacturing aid. If system margin is detected to be below normal at ambient temperature, this indicates the system may fail when heated. Thus, using the teaching of the present invention to exactly test system margin at an ambient temperature allows a prediction of system margin at higher temperature. This reduces the need to actually test the system in a heat chamber. 
     In addition, various embodiments of the present invention allow for a means to monitor the internal temperature within an integrated circuit. This information allows the lowering of operating frequency of the integrated circuit when the integrated circuit is at a temperature which is above a predetermined temperature limit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of a system in which signal delay through an integrated circuit is monitored in accordance with a preferred embodiment of the present invention. 
     FIG. 2 shows a block diagram of circuitry which performs signal delay monitoring through an integrated circuit in accordance with a preferred embodiment of the present invention. 
     FIG. 3 shows a block diagram of circuitry which performs signal delay monitoring through an integrated circuit in accordance with an alternate preferred embodiment of the present invention. 
     FIGS. 4,  5 ,  6  and  7  show timing diagrams for the circuitry shown in FIG. 2 in accordance with the preferred embodiment of the present invention. 
     FIG. 8 shows a timing diagram for the circuitry shown in FIG. 3 in accordance with the alternate preferred embodiment of the present invention. 
     FIG. 9 is a block diagram which shows regulation of operating frequency of an integrated circuit in accordance with a preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a block diagram of a system in which signal delay through a device under test (DUT)  11  is measured by a delay measuring device  12 , in accordance with a preferred embodiment of the present invention. A clock signal on a clock line  13  is used by both DUT  11  and delay measuring device  12 . Delay measuring device  12  uses the clock signal to measure an amount of delay introduced by DUT  11  to an output signal on an output pin  14 . 
     For example, DUT  11  is a Pentium processor available from Intel Corporation, having a business address of 3065 Bowers Ave., Santa Clara, Calif. 95051. For example, the output signal on output pin  14 , is the ADS# signal on a Pentium processor. In the preferred embodiment, the Pentium processor is in a fixed loop and has its interrupts turned off when measuring the output signal on output pin  14 . This is done in order to eliminate the possibility that the output signal on output pin  14  is varying with logic state within DUT  11 . 
     FIG. 2 shows an embodiment of delay measuring device  12 . A flip-flop  21  serves to provide a single clock cycle delay to the output signal on output pin  14  in order to produce a delayed signal on a line  28 . A gate  22  is controlled by the delayed signal on line  28 . When gate  22  allows the output signal on output pin  14  to pass through, the output signal charges an integrator consisting of a resistor  23  and a capacitor  25  connected to ground  26 , as shown. For example, resistor  23  has a resistance of 10 kilohms. Capacitor  25  has a capacitance of 0.1 microfarads. The operating frequency of the clock signal is, for example 33 megahertz. The integrator integrates a gated signal on a line  30  to produce an integrated signal on a line  29 . 
     An analog to digital converter  24  is used to convert the integrated signal on line  29  to a digital signal on an output line  27 . The digital signal on output line  27  is used by the system to, for example, determine system margin or as a temperature control feedback signal, as will be described in further detail below. 
     FIGS. 4,  5 ,  6  and  7  show timing diagrams for the circuitry shown in FIG. 2 in accordance with the preferred embodiment of the present invention. In FIG. 4, a waveform  51  shows the timing for the clock signal on clock line  13 . A waveform  52  shows the timing for the output signal on output pin  14 . A waveform  53  shows the timing for the delayed signal on line  28 . A waveform  54  shows the timing for the gated signal on line  30 . A waveform  55  shows the timing for the integrated signal on line  29 . Waveform  55  also shows the voltage of the integrated signal on line  29  relative to VCC represented by a line  58  and ground represented by a line  59 . In FIGS. 4 through 7, the changes in voltage of the integrated signal on line  29  relative to VCC represented by a line  58  and ground represented by line  59  are exaggerated to illustrate operation of the present invention. 
     In the example used to describe the preferred embodiment, the falling edge of the output signal on output pin  14  is required to occur after the rising edge of the clock signal and before the falling edge of the clock signal. Likewise, the rising edge of the output signal on output pin  14  is required to occur after the rising edge of the clock signal and before the falling edge of the clock signal. For operating conditions represented by FIG. 4, there is a significant system margin as illustrated by the rising edge of waveform  52  for the output signal on output pin  14  rising significantly before the falling edge of the clock signal represented by waveform  51 . This high system margin could result from a high system margin being designed into the system, favorable processing parameters and/or some combination of favorable operating parameters, such as low operating temperature and high VCC voltage level. 
     The resulting waveform  54  for the gated signal on line  30  illustrates that the integrator will charge capacitor  25  to a voltage which is relatively closer to VCC than to ground, as represented by waveform  55  for the integrated signal on line  29 . 
     In FIGS. 5,  6  and  7  as in FIG. 4, waveform  51  shows the timing for the clock signal on clock line  13 . Waveform  52  shows the timing for the output signal on output pin  14 . Waveform  53  shows the timing for the delayed signal on line  28 . Waveform  54  shows the timing for the gated signal on line  30 . Waveform  55  shows the timing for the integrated signal on line  29 . As discussed above, waveform  55  also shows the voltage of the integrated signal on line  29  relative to VCC represented by a line  58  and ground represented by line  59 . In FIGS. 5 through 7, the changes in voltage of the integrated signal on line  29  relative to VCC represented by a line  58  and ground represented by line  59  are exaggerated to illustrate the present invention. 
     For operating conditions represented by FIG. 5, the falling edge of the output signal on output pin  14  occurs relatively closer to the falling edge of the clock signal on clock line  13 , than for the operating conditions represented by FIG.  4 . Likewise, the rising edge of the output signal on output pin  14  occurs relatively closer to the falling edge of the clock signal on clock line  13 , than for the operating conditions represented by FIG.  4 . This indicates that the system margin has been reduced, for example, by a change in operating parameters, such as increased operating temperature and/or reduced VCC voltage level. 
     The resulting waveform  54  for the gated signal on line  30  is positive for a shorter duration than for the operating conditions represented by FIG.  4 . Also, the resulting waveform  54  for the gated signal on line  30  is negative for a longer duration than for the operating conditions represented by FIG.  4 . This will result in the integrator charging capacitor  25  to be charged less, and there will be a gradual decrease in voltage across the capacitor, as represented by waveform  55  for the integrated signal on line  29 . 
     For operating conditions represented by FIG. 6, the falling edge of the output signal on output pin  14  occurs right at the falling edge of the clock signal on clock line  13 . Likewise, the rising edge of the output signal on output pin  14  occurs right at the falling edge of the clock signal on clock line  13 . This indicates that there is no remaining system margin. This operating system could result from adverse operating parameters, such as increased operating temperature and/or reduced VCC voltage level. 
     The resulting waveform  54  for the gated signal on line  30  is about half the time positive and half the time negative. This will result in the integrator charging capacitor  25  to be about half way between VCC and ground, as represented by waveform  55  for the integrated signal on line  29 . 
     For operating conditions represented by FIG. 7, the falling edge of the output signal on output pin  14  occurs after the falling edge of the clock signal on clock line  13 . Likewise, the rising edge of the output signal on output pin  14  occurs after the falling edge of the clock signal on clock line  13 . This indicates that the integrated circuit no longer is within the specified delay requirements. This will likely result in a system failure. 
     The waveform  54  for the gated signal on line  30  is more often negative than positive. This will result in the integrator discharging capacitor  25 , and there will be a gradual decrease in voltage across the capacitor, as represented by waveform  55  for the integrated signal on line  29 . 
     The actual voltages shown in FIG. 4 through 7 are not to scale. Particularly, the DC component of the voltage for the integrated signal on line  29 , for some circuits, may differ only slightly (i.e., by hundreds of millivolts) over a range of various operating parameters for DUT  11 , dependent, for example, on the frequency of occurrence of transitions of the output signal on output pin  14 . A more complex filter, for example, could be used if desired to increase the ability to detect the voltage changes for the integrated signal on line  29 . Also, resolution could be improved by using different output pin signal with a minimum delay over the entire clock period. As discussed above, the output signal on output pin  14  is required to transition during the first half of the clock cycle. 
     FIG. 3 shows an alternative embodiment of circuitry which monitors delay of the output signal on output pin  14 . In the embodiment shown in FIG. 3, delay in transition of both the falling edge and the rising edge of the output signal on output pin  14  is utilized in deriving the voltage on an integrated signal on line  49 . This increases the number of samples of the output signal on output pin  14  when compared with the circuitry in FIG.  2 . For the circuitry shown in FIG. 2, only the falling edge of the output signal on output pin  14  is utilized in deriving the voltage of the integrated signal on line  29 . 
     A flip-flop  31  serves to provide a single clock cycle delay to the output signal on output pin  14 , inverted by an inverter  32 . Flip-flop  31  produces a Q output on a line  39  and an inverted Q output. A logic NAND gate  33  combines the inverted output signal, the inverted Q output and the clock signal to produce a charge signal on a line  40 . The charge signal is used to control a gate  37 . Gate  37  gates VCC on line  35  to the input of an integrator, further described below. A logic NAND gate  34  combines the inverted output signal, the Q output and the clock signal to produce a discharge signal on a line  41 . The discharge signal is used to control a gate  38 . Gate  37  gates a reference voltage (ground)  36  to the input of the integrator described below. 
     The integrator includes a resistor  42 , a resistor  43  a capacitor  44  and a capacitor  45 . Capacitors  44  and  45  are connected to ground  36 , as shown. For example, resistor  42  has a resistance of 100 kilohms. Resistor  43  has a resistance of 10 kilohms. Capacitor  44  has a capacitance of 0.01 microfarads. Capacitor  45  has a capacitance of 0.1 microfarads. 
     An amplifier is used to stabilize the integrated signal on line  49 . The amplifier includes an operational amplifier  48  and a resistor  47 . For example, resistor  47  has a resistance of 100 kilohms. 
     FIG. 8 shows a timing diagram for the circuitry shown in FIG. 3 in accordance with the preferred embodiment of the present invention. In FIG. 8, a waveform  61  shows the timing for the clock signal on clock line  13 . A waveform  62  shows the timing for the output signal on output pin  14 . A waveform  63  shows the timing for a Q output on line  39 . A waveform  66  shows the timing for the charge signal on line  40 . A waveform  67  shows the timing for the discharge signal on line  41 . A waveform  65  shows the timing for the integrated signal on line  49 . Waveform  65  also shows the voltage of the integrated signal on line  49  relative to VCC represented by a line  68  and ground represented by line  69 . 
     As described above, the voltage of integrated signal on line  49  can be converted to a digital signal which is periodically read and then averaged to obtain a value which indicates the amount of delay of the output signal on output pin  14 . Alternately, the amount of delay can be obtained directly from measuring the voltage value of the integrated signal on line  49 . By comparing the delay set out in the manufacturers specifications for the DUT  11  with the measured delay on the output signal on output pin  14 , the system margin for the integrated circuit is determined. To optimize DUT  11 , the operating frequency can be increased up to a new system margin selected by the user of DUT  11 . 
     The present invention also allows for the sensing of the core temperature of an integrated circuit by externally monitoring the phase delay of signals propagating through the integrated circuit, for example, by monitoring the change in the delay on the output signal on output pin  14 . As the operating temperature rises, the phase delay will increase. 
     In the preferred embodiment, the value of the voltage of the integrated signal (and thus the detected phase delay of the output signal) is calibrated for each individual DUT  11 . In order to do this, a thermal performance test of one or more test devices of the same type as DUT  11  is first performed. In this test, the value of the voltage of the integrated signal is detected at various operating temperatures of the test device. For example, the voltage of the integrated signal is measured when the test device is at ambient temperature, at a maximum temperature, and at several temperatures in between. This gives a continuous relationship between operating temperature of the test device and the voltage of the integrated signal for the test device. This gives a “curve” which describes the general relationship between operating temperature of the test device and the voltage of the integrated signal. The form of the “curve” is generally the same for all test devices with identical circuitry to the test integrated circuit For each new device, the value of the voltage of the integrated signal is measured under two or more operating conditions under which the operating temperature is known from the actual values measured for the test device in order to have reference points with which to “fit” to the curve determined using the test integrated circuit. 
     FIG. 9 shows a block diagram of a system in which signal delay through a device  71  is measured by a phase delay detection device  72 , as described above. For example, one of the implementations of delay measuring device  12  shown in FIG. 2 or FIG. 3 is used to implement phase delay detection device  72 . 
     A clock signal on a clock line  75  is used by both device  71  and phase delay detection device  72 . Phase delay detection device  72  uses the clock signal to measure an amount of delay introduced by device  71  to an output signal on an output pin. The signal generated by phase delay detection device  72  is used by a control signal generator  73  to control a switch line connected to a fast/slow line of a clock generator circuit  74 . In essence, control signal generator  73  measures voltage from the output of delay detection device  72  and creates an output signal which controls clock generator circuit  74 . Control signal generator  73  is implemented, for example, by a comparator with a setable threshold. For example, in the preferred embodiment, control signal generator  73  controls voltage of pin number  11  (SCLK22) of an Avasem AV9155-02 clock generator available from Integrated Circuit Systems, Inc. having a business address of 1275 Parkmoor Avenue San Jose, Calif. 95126-3448. 
     Clock generator circuit  74  produces a 66.6 megahertz clock when pin number  11  is asserted high, and produces a 16 megahertz clock when pin number  11  is de-asserted low. Thus when the voltage of the signal generated by phase delay detection device  72  increases above a selected threshold, clock generator circuit  74  will reduce the operating speed of the processor from 66.6 megahertz to 16 megahertz. For example, in the preferred embodiment, device  71  is a Pentium processor and the selected threshold of the voltage of the signal generated by phase delay detection device  72  is selected so that the Pentium processor will be slowed down when an increase in temperature results in the measured delay on the output signal on the output pin of device  71  increasing past an acceptable value. This will prevent the device  71  from failing as a result of temperature overheating. 
     The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.