Driver circuit with temperature correction circuit

A driver circuit having a temperature correction circuit for producing an output signal with high precision amplitude and timing by correcting the temperature changes in the amplitude and timing. The temperature correction circuit includes a temperature detector for detecting the temperature change in output elements, a timing adjustment circuit for correcting the timing of an output signal relative to an input signal upon receiving the temperature detection signal from the temperature detector, and a bias circuit for correcting the output amplitude and impedance of the output signal.

FIELD OF THE INVENTION 
This invention relates to a temperature correction circuit for a driver 
circuit which outputs pulse signals to be used in electrical instruments, 
and more particularly, to a temperature correction circuit used in a 
driver circuit which is capable of generating an output signal having a 
stable and high accuracy amplitude and timing in spite of temperature 
changes in the driver circuit. 
BACKGROUND OF THE INVENTION 
FIG. 4 is a block diagram showing an example of the last stage of a driver 
circuit in the conventional technology having a complementary 
configuration. In this example, the last stage of the driver circuit is 
comprised of a bias circuit 40, output elements 31 and 32, and an 
impedance matching resistor 4. FIG. 5 shows a more detailed structure of 
the driver circuit of FIG. 4 which is used, for example, as a pin driver 
circuit in a test channel of a semiconductor test system. In such a 
semiconductor test system, the pin driver circuit is to apply a test 
signal to a corresponding one of device pins of a semiconductor device 
under test (DUT). The example of driver circuit in FIG. 5 has no 
temperature correction circuit. 
The output elements 31 and 32 in this example are formed with CMOS transfer 
gates. The output elements 31 and 32 in the last stage of the driver 
circuit consumes a large portion of the power consumption of the driver 
circuit. The amount of the power consumption varies depending on waveforms 
of pulse signals provided to the output elements as well as operating 
speeds of the output elements. Because of the changes in the power 
consumption, junction temperature of the output elements also changes, 
which fluctuates the performance of the driver circuit. Consequently, the 
output amplitudes and edge timings vary from what originally intended. 
FIG. 6 shows an example of drain current curves versus gate voltages in the 
output element formed with CMOS transfer gates when the temperature 
changes. In general, when the temperature in the MOS transistor devices 
increases, a threshold voltage denoted by Vt and drain current denoted by 
Id will decrease. As a result, the drain current Id at the bias point 9 of 
FIG. 6 decreases. Because of this characteristics, a problem arises in the 
conventional driver circuit that an output voltage level drops with an 
elapse of time as shown in FIG. 7A. 
Such an output voltage change caused by the temperature change in the 
output element increases with the increase in the amount of output current 
flowing to the load. This is because an output impedance of the output 
element varies with the increase of the temperature, and the output 
voltage is a product of the output current and the output impedance. 
FIGS. 7B-7D show examples of timing deviation between an input signal and 
an output signal. FIG. 7C shows an intended delay timing of the output 
signal with respect to the input signal of FIG. 7B. FIG. 7C shows an 
additional delay time .DELTA.t occurred in the output signal with respect 
to the input signal of FIG. 7B because of the temperature rise in the 
output element. In this manner, the timing deviation in the output signal 
occurs when the temperature in the driver circuit changes. Accordingly, 
the present invention is directed to a driver circuit which is able to 
maintain the output impedance of the driver circuit constant as well as to 
maintain a signal propagation delay time constant. 
For a driver circuit that requires a high degree of precision, an external 
apparatus must be installed to keep the temperature of an area surrounding 
the driver circuit in a constant value. Examples of such external apparats 
is a cooler or an air conditioner, which increases the cost and size of 
the driver circuit. 
As explained in the foregoing, in the driver circuit without a temperature 
compensation capability, the output amplitudes and timings deviate from 
what originally intended because of the temperature change. Basically, 
such a temperature change is caused by the change in the power consumption 
in the output elements 31 and 32 in the driver circuit. Consequently, the 
driver circuit in the conventional technology is not able to produce 
output signals having amplitudes and timings with sufficient precision. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a driver 
circuit with a temperature correction capability for generating output 
signals having amplitudes and timings with high stability. 
It is another object of the present invention to provide a driver circuit 
having a temperature correction circuit which detects the temperature 
changes in output elements in the last stage of the driver circuit and 
compensates the temperature changes in the driver circuit. 
It is a further object of the present invention to provide a variety of 
ways to detect the temperature changes in the output elements of the 
driver circuit or the temperature change in the driver circuit as a whole 
and compensates the temperature changes. 
The temperature correction circuit of the present invention is based on the 
fact that the heat source in the driver circuit is primarily concentrated 
on the power consumed by the output elements of the driver circuit. 
In one aspect of the present invention, the temperature correction circuit 
for the driver circuit includes: a temperature detector for detecting 
temperature variations in output elements or in a driver circuit chip as a 
whole; an output timing correction circuit for correcting output timing 
changes caused by the temperature variations in an output signal relative 
to an input signal when receiving the temperature detection signal from 
the temperature detector; and an output amplitude correction circuit for 
correcting output amplitude changes caused by the temperature variations 
in the output signal when receiving the temperature detection signal from 
the temperature detector. 
By this arrangement, the temperature correction circuit is achieved for the 
driver circuit having output elements complementarily connected with each 
other. The driver circuit receives an input signal and generates an output 
signal of a predetermined output amplitude and timing. The driver circuit 
of the present invention can provide the output signal of highly 
stabilized amplitude and timing even though the temperature of the output 
elements changes. 
One of the examples of temperature detector is a voltage measurement 
circuit which measures voltages representing electric currents flowing 
through the output elements. Alternatively, the temperature detector may 
be a temperature sensor which is provided in close proximity to the output 
elements in the driver circuit. Further, the temperature detector may be a 
temperature sensor for detecting the temperature of the driver circuit 
chip as a whole. 
An example of the output timing correction circuit is a plurality of series 
connected gate circuits which vary their signal propagation delay time 
when receiving the temperature detection signal from the temperature 
detector. The positive and negative source voltages for the series 
connected gates are regulated based on the temperature detection signal, 
thereby controlling the signal propagation delay time in the series 
connected gates for correcting the timings of the output signal. 
An example of the output amplitude and impedance correction circuit is a 
bias circuit which changes the signal amplitude when receiving the 
temperature detection signal from the temperature detector. The positive 
and negative source voltages for the bias circuit are regulated based on 
the temperature detection signal, thereby controlling the signal amplitude 
of the output signal relative to the input signal for correcting the 
amplitude and impedance change caused by the temperature change. 
More specifically, the example of configuration of the driver circuit 
having the temperature correction circuit includes detection resistors 33 
and 34 for detecting electric current flowing through the output elements 
31 and 32, and electric power monitor circuits 35 and 36 for monitoring 
the temperature (current) of the output elements 31 and 32 based on the 
voltages across the detection resistors 33 and 34. The driver circuit 
further includes correction circuits 37 and 38 for generating correction 
signals 51, 52, 53 and 54 to be provided to a timing adjustment circuit 39 
and to a bias circuit 40, respectively, when receiving temperature 
detection signals 22 and 23 from the electric power monitor circuits 35 
and 36. The timing adjustment circuit 39 is provided for adjusting the 
timing of the output signal 3 relative to the input signal 1 when 
receiving the correction signals 53 and 54 from the correction circuits 37 
and 38 to correct the changes in the output signal timing caused by the 
temperature changes. The bias circuit 40 is provided for generating the 
amplitude corrected output signal to the output elements 31 and 32 when 
receiving the correction signals 51 and 52 from the correction circuits 37 
and 38, thereby establishing the output amplitude and impedance correction 
circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a block diagram showing a driver circuit having a temperature 
correction circuit of the present invention. FIG. 2 is a circuit diagram 
showing a more detailed circuit structure of the driver circuit having the 
temperature correction circuit of the present invention. FIGS. 3A-3D show 
input and output voltage relationships for explaining a principle of 
temperature correction of the present invention. 
The basic principle of temperature correction is explained with reference 
to FIG. 3A-3D which show input/output characteristics with respect to the 
temperature changes. FIG. 3A shows an ideal characteristic required as an 
output voltage signal wherein the output voltage level is proportional to 
the input voltage level in a constant manner. FIG. 3B shows a situation 
where the relationship between the input voltage and the output voltage is 
non-linear due to the heat dissipated by the junctions of the output 
elements 31 and 32. In response to this non-linear relationship of FIG. 
3B, the present invention establishes a correction curve of input/output 
relationship as shown in FIG. 3C in the temperature correction circuit. 
The correction curve is inverse to the non-linear relationship of FIG. 3B. 
Therefore, the output/input voltage relationship is corrected to be almost 
a straight line as shown in FIG. 3D to reduce the adverse effects by the 
temperature change. 
The driver circuit having the temperature correction function of the 
present invention is explained in the following with reference to FIG. 1. 
The driver circuit is formed with output elements 31 and 32, electric 
current detection resistors 33 and 34, differential amplifiers 33b and 
34b, electric power monitor circuits 35 and 36, correction circuits 37 and 
38, a timing adjustment circuit 39 and a bias circuit 40. 
The electric current detection resistors 33 and 34 are resistance to detect 
electric current flowing through the corresponding output elements 31 and 
32. The differential amplifiers 33b and 34b are provided to stabilize the 
electric voltage supplied to the corresponding voltage source terminals of 
the output elements 31 and 32. 
The electric power monitor circuits 35 and 36 detect voltage drops across 
the electric current detection resistors 33 and 34, respectively. The 
monitor circuits 35 and 36 provide temperature detection signals 22 and 23 
to the correction circuits 37 and 38, respectively. The correction 
circuits 37 and 38 receive the respective temperature detection signals 22 
and 23, and generate correction signals 51, 52, 53 and 54 as voltage 
sources (ViH, ViL) to be provided to the timing adjustment circuit 39 and 
the bias circuit 40. 
The timing adjustment circuit 39 has a variable delay time function 
therein. When receiving the delay time correction signals 53 and 54 from 
the correction circuits 37 and 38, respectively, the timing adjustment 
circuit 39 adjusts delay times of drive signals 41 and 42 therefrom to be 
provided to the output elements 31 and 32 through the bias circuit 40. 
The bias circuit 40 has a variable amplitude function therein. When 
receiving the amplitude correction signals 51 and 52 from the correction 
circuits 37 and 38, respectively, the bias circuit 40 provides drive 
signals having corrected amplitude levels to the input terminals of the 
corresponding output elements 31 and 32. 
The more detailed example of the driver circuit corresponding to the 
schematic block diagram of FIG. 1 is shown in FIG. 2. In this example, the 
output elements 31 and 32 are formed with CMOS transfer gates. The timing 
adjustment circuit 39 has a level shifter and a variable delay circuit. 
The variable delay circuit in this example has a plurality of series 
connected CMOS gates which receive the correction signals 53 and 54 as 
voltage sources. By regulating the value of voltage sources to the 
plurality of CMOS gates, the signal propagation delay time between the 
input signal and the output signal for the plural CMOS gates is 
fine-adjusted to establish the variable delay time circuit. The level 
shifter 2 is a circuit to produce a differential output signal upon 
receiving an input signal 1 and shifts the voltage level of the 
differential output signal therefrom. 
The bias circuit 40 receives drive signals 41 and 42 from the timing 
adjustment circuit 39 and regulates the amplitude of the driver signals 
based on the correction signals (voltage sources) 51 and 52 from the 
correction circuits 37 and 38. An example of the bias circuit 40 includes 
a pair of CMOS gate circuits as shown in FIG. 2. The pair of CMOS gate 
circuits receives the drive signals 41 and 42, respectively. The 
amplitudes of the drive signals 41 and 42 are regulated by the value of 
voltage sources 51 and 52 to the pair of CMOS gate circuits. 
In the electric power monitor circuits 35 and 36, integration circuits 20 
and 21 respectively integrate periodic voltage signals detected by the 
current detection resistors 33 and 34. The integration circuits 20 and 21 
provide resultant average voltage signals to the correction circuits 37 
and 38 as temperature detection signals 22 and 23, respectively. 
In receiving the temperature detection signals 22 and 23 from the electric 
power monitor circuits 35 and 36, the correction circuits 37 and 38 
provide the correction signals 51, 52, 53 and 54 which work as source 
voltages (ViH, ViL) to the timing adjustment circuit 39 and the bias 
circuit 40. Each of the correction circuits 37 and 38 is formed, for 
example, of a correction coefficient circuit, an adder circuit, and a 
subtraction circuit. 
The correction coefficient circuits K43, K44, K45 and K46 in the correction 
circuits 37 and 38 are to fine adjust the curves when receiving the 
signals from electric power monitor circuit 35 and 36. The correction 
coefficient circuits K43-K46 adjust gains and curves of the non-linear 
characteristics of the output temperature timing and output temperature 
amplitude of the output elements 31 and 32. Preferably, the correction 
coefficients are pre-adjusted before being installed in the driver 
circuit. 
An example of the correction circuit is shown in FIG. 13 which is directed 
to a partial circuit configuration corresponding to the left portion of 
the correction circuit 37. In this example, operational amplifiers 82 and 
84 and resistors 85-89 are used. The resistors 85-89 are connected to the 
operational amplifiers 82 and 84 in the manner as shown in FIG. 13 to form 
the inverting amplifiers series connected with one another. The 
temperature detection signal 22 from the power monitor circuit 35 and the 
positive voltage source ViH is added at the input of the first inverting 
amplifier to combine the two input signals. The output of the amplifier 84 
is provided to the timing adjustment circuit 39 of FIG. 2 as a control 
signal. 
Although not shown, the correction circuit of FIG. 13 may include a 
non-linear element such as a diode to establish a curve such as shown in 
FIG. 3C to compensate the non-linear characteristics of the output 
elements 31 and 32. By the correction circuits, signals corrected in the 
gain/curves are provided to the timing adjustment circuit 39 and bias 
circuit 40. 
The correction circuits 37 and 38 provide correction signals (voltage 
sources) to the timing adjustment circuit 39 and bias circuit 40 as 
correction signals. Based on the value of voltage sources to the plurality 
of CMOS gates in the timing adjustment circuit 39, the signal propagation 
delay time between the input signal and the output signal for the plural 
gates is controlled. Similarly, based on the value of voltage sources 
provided to the bias circuit 40, the amplitude of the drive signals 41 and 
42 is controlled. Thus, the timing adjustment circuit 39 carries out the 
function of fine adjusting the signal propagation delay times in the 
plurality of gates, and the bias circuit 40 carries out the function of 
fine adjusting the amplitude of the signals to be provided to the output 
elements 31 and 32. 
Because of the configuration of the present invention noted above, in 
response to the temperature changes due to the electric power consumption 
in the output elements 31 and 32, the resultant changes in the output 
amplitude and impedance or the change in the output signal timing can be 
corrected. As a consequence, the driver circuit is able to produce output 
amplitudes and timings with high precision and stability. 
In the foregoing embodiment shown in FIG. 2, the driver circuit utilizes 
CMOS gates. However, it is also possible to form the driver circuit with 
other semiconductor circuits such as a bipolar circuit accompanied by 
peripheral circuits suitable for the bipolar circuit. 
In the foregoing explanation of the embodiment of the present invention, 
the temperature changes of the output elements 31 and 32 are detected by 
the electric power monitor circuits 35 and 36 by measuring the voltage 
drops across the resistors 33 and 34. However, it is also possible to 
detect the temperature change by other sensors such as a thermostat or a 
posistor provided close to the output elements 31 and 32. Furthermore, it 
is possible to include a temperature sensor for detecting the temperature 
of the IC chip as a whole and the detected result may be combined with the 
detected temperature of the output elements 31 and 32. 
Such various ways of temperature sensing are shown in FIGS. 8-11. FIG. 8 is 
a block diagram showing the driver circuit of the present invention having 
a temperature sensor for detecting temperature changes in one of the 
output elements. A temperature sensor 91 is provided in close proximity to 
the output element 31 to detect the temperature of the output element 31. 
In this example, the output of the temperature sensor 91 is directly 
supplied to the correction circuits 37 and 38 to control the output timing 
and the output amplitude of the driver circuit. 
FIG. 9 is a block diagram showing the driver circuit of the present 
invention having a temperature sensor for detecting temperature changes 
common to both of the output elements. A temperature sensor 93 is provided 
in close proximity to both the output elements 31 and 32 to detect the 
temperature of the output elements 31 and 32. If the overall size of the 
driver circuit is small enough, the temperature sensor 93 may also 
function to sense the temperature of the driver circuit as a whole. In 
this example, the output of the temperature sensor 93 is directly supplied 
to the correction circuits 37 and 38 to control the output timing and 
amplitude of the driver circuit. 
FIG. 10 is a block diagram showing a driver circuit of the present 
invention having a pair of temperature sensors for detecting temperature 
changes in the output elements and a pair of adder circuits for combining 
the output signals of the temperature sensors and the output signals of 
the power monitor circuit showing the amounts of current flowing through 
the output elements. A temperature sensor 91 is provided to sense the 
temperature change in the output element 31. A temperature sensor 92 is 
provided to sense the temperature change in the output element 32. 
The output signals of the temperature sensor 91 and of the power monitor 
circuit 35 are combined by an adder circuit 95 whose output is provided to 
the correction circuit 37. The output signals of the temperature sensor 92 
and of the power monitor circuit 36 are combined by an adder circuit 96 
whose output is provided to the correction circuit 38. Since the 
arrangement of FIG. 10 can regulate the output timing and amplitude based 
on the current flowing in the output elements as well as the temperature 
of the output elements, it is expected that more precise temperature 
correction is achieved in the driver circuit. 
FIG. 11 is a block diagram showing a driver circuit of the present 
invention having a temperature sensor further to the pair of temperature 
sensors and the pair of adder circuits of FIG. 10. In this example, a 
temperature sensor 94 is additionally provided to sense the temperature of 
the driver circuit as a whole. The output signal of the temperature sensor 
94 is supplied to the adder circuit 95 to be combined with the output 
signals from the temperature sensor 91 and the power monitor circuit 35. 
The output signal of the temperature sensor 94 is also supplied to the 
adder circuit 96 to be combined with the output signals from the 
temperature sensor 92 and the power monitor circuit 36. 
An example of temperature sensor to be used in the foregoing examples of 
FIGS. 8-11 is shown in FIG. 12. In this example, the temperature sensor is 
formed with a constant current source 74, a temperature sensitive PN 
junction 76 and a buffer 74. The PN junction 76 is forward biased by the 
constant current source 74 and a threshold voltage of the PN junction is 
detected by the buffer 74. The threshold voltage of the PN junction varies 
in response to the temperature changes. Thus, the change in the output 
voltage of the buffer 74 represents the temperature surrounding the PN 
junction 76. 
In the foregoing explanation of the embodiment, the timing adjustment 
circuit 39 has the input signal 1 through a single input line. However, it 
is also possible to establish the timing adjustment circuit 39 in such a 
way as to receive an input signal through differential input terminals 
while eliminating the level shifter 2. 
In the explanation for the embodiment of the present invention, the 
temperature correction is achieved with an emphasis on the temperature 
changes in the output elements 31 and 32. However, it is also possible to 
achieve the purpose of the present invention by adjusting the correction 
coefficient circuits K43, K44, K45 and K46 to compensate the overall 
temperature characteristics of the driver circuit including the timing 
adjustment circuit 39, the bias circuit 40, the correction circuits 37 and 
38, and the electric power monitor circuits 35 and 36. 
Further, in the foregoing explanation of the embodiment of the present 
invention, the electric power monitor circuits 35 and 36 or the 
temperature sensor such as the thermostat or a posistor is provided to 
detect the temperature changes in the output elements 31 and 32, and 
detection signals are provided to the correction circuits 37 and 38, 
respectively. In other words, in the foregoing examples, two systems of 
detection signals are feedbacked to the corresponding two systems of 
correction circuits. However, it is also possible to achieve the object of 
the present invention by having a single feedback system with one 
detection signal and one correction circuit for focusing on only one of 
the output elements 31 and 32. This enables to simplify the circuit 
configuration of the driver circuit in case where either one of the high 
or low output signals are mainly used. 
In the foregoing explanation of the embodiments, the temperature change of 
the output elements 31 and 32 is detected by electric power monitor 
circuits 35 and 36 or temperature sensor such as the thermostat and 
posistor. That is, two types of detection signal are provided. However, it 
is also possible to use only one type of representative detection signal 
to be given to the correction circuit. For example, a temperature sensor 
can be arranged to a sense point that is common to both output elements 31 
and 32 to take out a detection signal representative of both output 
elements. Moreover, the output signal of electric power monitor circuits 
35 and 36 can be averaged and used as a representative detection signal. 
This enables to simplify the circuit configuration of the present 
invention when the high level and low level circuits in the driver circuit 
are used in substantially the same manner. 
Because of the temperature correction voltages from the correction circuits 
37 and 38, the signal propagation delay time between the input and output 
of the plural gates connected in series in the timing correction circuit 
39 is adjusted. Consequently, the temperature dependency in the output 
timing of the output signal 3 can be significantly reduced. 
Because of the temperature correction voltages from the correction circuits 
37 and 38, the amplitude and impedance in the amplitude and impedance 
correction circuit 40 is adjusted. Consequently, the temperature 
dependency in the output amplitude and impedance of the output signal 3 
can be significantly reduced. 
As a result, the fluctuation in the output signal amplitude, the output 
impedance and the output timing can be corrected in response to the change 
in the heat dissipation caused by the electric consumption in the output 
elements 31 and 32. Thus, a driver circuit of precise and stable signal 
amplitude and precise timing can be realized. Moreover, unlike the 
conventional technology, it is possible to obviate the use of a forceful 
cooler or an air conditioner or cooling system to maintain the temperature 
surrounding the driver circuit constant. 
Although only preferred embodiments are specifically illustrated and 
described herein, it will be appreciated that many modifications and 
variations of the present invention are possible in light of the above 
teachings and within the purview of the appended claims without departing 
the spirit and intended scope of the invention.