Patent Abstract:
An apparatus includes an integrated circuit that includes low side power supply circuitry that provides an output voltage for H-bridge circuitry. The low side power supply circuitry includes one transistor that provides one current to the output of the low side power supply circuitry in response to the output voltage of the low side power supply circuitry dropping below a quiescent level. The low side power supply circuitry also includes a second transistor that controls the conduction state of a third transistor, based at least in part, upon the first transistor providing the first current to the output of the low side power supply circuitry. The third transistor provides a second current to the output of the low side power supply circuitry.

Full Description:
RELATED APPLICATION AND TECHNICAL FIELD  
       [0001]     This application is related to the following U.S. application, of common assignee, from which priority is claimed, and the contents of which are incorporated herein in their entirety by reference: “High Voltage CMOS H-Bridge Gate Drive Power Supplies,” U.S. Provisional Patent Application Ser. No. 60/661,754, filed Mar. 15, 2005.  
         [0002]     This disclosure relates to power supplies for power amplifiers and, more particularly, to driving H-Bridge transistors at relatively high speed without components located off-chip. 
     
    
     BACKGROUND  
       [0003]     Some types of power amplifiers such as pulse width modulated (PWM) amplifiers include a network of switching elements for controlling the directional flow of output current into a load. By outputting currents that alternate in direction, PWM amplifiers drive direct current (DC) and stepper motors for motion control applications in robotics, servomechanisms, printing devices, etc.  
         [0004]     To provide currents with alternating flow directions, some PWM amplifiers implement four switching elements that provide two output currents with different flow directions. This circuitry, known as an “H-Bridge”, may include various types of electronic components (e.g., relays, transistors, etc.) to provide the four switching elements.  
         [0005]     To control H-Bridge operations, the PWM amplifier produces a pulse train that controls the functioning of the electronic switching components. For example, an external signal provided to a PWM amplifier may control the duty cycle of the pulse train. To initiate current flow in one direction, the duty cycle of the pulse train is increased to one pair of switching elements while the duty cycle of a complementary pair of switching elements is reduced.  
         [0006]     Conventional PWM amplifiers implemented in monolithic integrated circuits (ICs) typically implement n-channel transistors and are typically unable to independently provide appropriate signal levels for controlling H-Bridge operations. To attain the appropriate signal levels, such PWM amplifiers use transistors implemented as source followers to “pull-up” signal levels. These pull-up transistors are typically coupled using relatively large capacity capacitors, known as bootstrap capacitors. Due to their large storage capacity, these bootstrap capacitors are typically located external to the IC. By implementing pull-up transistors and bootstrap capacitors, design complexity and production cost increases.  
       SUMMARY OF THE DISCLOSURE  
       [0007]     In accordance with an aspect of the disclosure, an apparatus includes an integrated circuit that includes low side power supply circuitry that provides an output voltage for H-bridge circuitry. The low side power supply circuitry includes one transistor that provides one current to the output of the low side power supply circuitry in response to the output voltage of the low side power supply circuitry dropping below a quiescent level. The low side power supply circuitry also includes a second transistor that controls the conduction state of a third transistor, based at least in part, upon the first transistor providing the first current to the output of the low side power supply circuitry. The third transistor provides a second current to the output of the low side power supply circuitry.  
         [0008]     In accordance with another aspect of the disclosure, an apparatus that includes an integrated circuit that includes high side power supply circuitry that provides an output voltage for H-bridge circuitry. The high side power supply circuitry includes a transistor configured to draw a first current from the output of the high side power supply circuitry in response to the output voltage of the high side power supply circuitry exceeding a quiescent level. The high side power supply also includes a second transistor that controls the conduction state of a third transistor, based at least in part, upon the first transistor drawing the first current from the output of the high side power supply circuitry. The third transistor draws a second current from the output of the high side power supply circuitry.  
         [0009]     In accordance with still another aspect of the disclosure, an apparatus includes an integrated circuit that includes low side power supply circuitry that provides an output voltage for H-bridge circuitry. The low side power supply circuitry includes a transistor that provides a first current to the output of the low side power supply circuitry in response to the output voltage of the low side power supply circuitry dropping below a quiescent level. The low side power supply also includes a second transistor that controls the conduction state of a third transistor, based at least in part, upon the first transistor providing the first current to the output of the low side power supply circuitry. The third transistor provides a second current to the output of the low side power supply circuitry. The integrated circuit also includes high side power supply circuitry that provides an output voltage for the H-bridge circuitry. The high side power supply circuitry includes a fourth transistor that draws a first current from the output of the high side power supply circuitry in response to the output voltage of the high side power supply circuitry exceeding a quiescent level. The high side power supply circuitry also includes a fifth transistor that controls the conduction state of a sixth transistor based, at least in part, upon the fourth transistor drawing the first current from the output of the high side power supply circuitry. The sixth transistor draws a second current from the output of the high side power supply circuitry.  
         [0010]     In accordance with still another aspect of the disclosure, a method includes a transistor, sending a first current to an output of a low side power supply circuitry in response to the output voltage of the low side power supply circuitry dropping below a quiescent level. The low side power supply circuitry provides an output voltage for H-bridge circuitry. The method also includes a second transistor, sending a second current to the output of the low side power supply circuitry, based at least in part, upon the first transistor sending the first current to the output of the low side power supply circuitry. A third transistor controls the conduction state of the second transistor.  
         [0011]     Additional advantages and aspects of the present disclosure will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present disclosure is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a block diagram representing a pulse width modulation amplifier.  
         [0013]      FIG. 2  is a block diagram representing a portion of the H-Bridge controller included in the PWM amplifier shown  FIG. 1 .  
         [0014]      FIG. 3  is one exemplary circuit used to implement the low side driver power supply shown in  FIG. 2 .  
         [0015]      FIG. 4  is one exemplary circuit used to implement the high side driver power supply shown in  FIG. 2 .  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0016]      FIG. 1  is a block diagram of a pulse width modulation (PWM) power amplifier  100  according to one embodiment. In this exemplary embodiment, PWM amplifier  100  includes Control Logic and PWM Generator Circuitry  102 , H-bridge Controller Circuitry  104 , and H-bridge Circuitry  106  that provides the output of the PWM amplifier.  
         [0017]     PWM amplifier  100  may provide an output current that may alternate between two flow directions. For example, a current that flows in one direction to a load may be provided during one time period and another current that flows in an opposite direction may be provided during another time period. Control Logic and PWM Generator Circuitry  102  may be connected to a plurality of inputs  108  for receiving one or more input signals. For example, Control Logic and PWM Generator Circuitry  102  may receive one or more input signals, for defining output current limits, for timing, and/or for reference (e.g., a reference voltage signal) and/or protection (e.g., a short circuit alert signal).  
         [0018]     Control Logic and PWM Generator Circuitry  102  may produce one or more control signals that may be provided to H-bridge Controller Circuitry  104 . For example, a PWM signal may be provided by Control Logic and PWM Generator Circuitry  102  to H-bridge Controller Circuitry  104 . Based on these control signals, H-bridge Controller Circuitry  104  may produce one or more signals for driving, e.g., switching elements included in H-bridge Circuitry  106 . For example, signals for biasing bipolar (e.g., bipolar junction transistors, etc.) and/or field-effect switching elements (e.g., field-effect transistors, complementary metal oxide semiconductor (CMOS) transistors, etc.) may be provided by H-bridge Controller Circuitry  104 . By providing appropriate driver signals to H-Bridge Circuitry  106 , PWM amplifier  100  may provide current signals that may flow in alternate directions to one or more loads connected to outputs  110 .  
         [0019]      FIG. 2  is a detailed diagram of one embodiment of H-bridge Controller Circuitry  104  that implements complementary polarity metal-oxide semiconductor (MOS) transistors. H-bridge Controller Circuitry  104  may include power supply circuitry  202 , a high side driver  204  and a low side driver  206 . Low side driver  206  may deliver pulses to switching elements (e.g., N-channel power transistors) that may be located in H-bridge Circuitry  106 . In one design, pulses ranging between 0 volt to +20 volts may be provided to the low side switching elements over conductors  208  and  210 . Similarly, high side driver  204  may deliver pulses to complementary switching elements (e.g., P-channel transistors) that may be located in H-bridge stage  106 . To control these switching elements, pulses ranging between +60 volts and +40 volts may be provided over conductors  212  and  214  to the respective switching elements.  
         [0020]     To provide power, e.g., a low side power supply  216  may be connected to low side driver  206  and a high side power supply  218  may be connected to high side driver  204 . Additionally, a source power supply  220  (e.g., +60 volts power supply) may be connected to high side driver  204  and power supplies  216  and  218 . Low side power supply  216  may approximately provide a +20 volt level to low side driver  206  and current as indicated by label I 1 . In a similar manner, high side power supply  218  may approximately provide a +40 volt level to high side driver  204 . However, as illustrated with label I 2 , power supply  218  may sink current. Additionally, power supply  218  may regulate a 20 volt level below the +60 volt level that may be provided by source power supply  220 . By regulating the voltage provided to high side driver  204 , the design may substantially prevent over-driving components in H-bridge Circuitry  106 . For example, by regulating the voltage, switching elements (e.g., P-channel transistors) in H-Bridge Circuitry  106  may be substantially prevented from exceeding a maximum gate breakdown voltage rating.  
         [0021]     For demonstrative purposes, exemplary pulse trains  222  and  224  may be respectively provided by high side driver  204  and low side driver  206  to the appropriate switching elements in H-Bridge stage  106 . Pulse train  222  may be limited to voltage levels between +60 volts and +40 volts for controlling switching operations of e.g., P-channel power transistors, while pulse train  224  may provide approximately +20 volt pulses for controlling the switching operations of e.g., N-channel power transistors in H-bridge Circuitry  106 .  
         [0022]     Conventional designs that implement N-channel transistors may include relatively large energy storage capacitors (i.e., bootstrap capacitors) that may be located external to the IC package containing the PWM amplifier. These additional components may increase production cost and design complexity. By implementing H-bridge controller circuitry that includes complementary metal oxide semiconductor (CMOS) technology, external energy storage components may be eliminated and production cost and design complexity may be reduced. By implementing power supplies with reduced output capacitance and relatively high operating speeds, H-bridge Controller Circuitry  104  (e.g., high side driver  204 , low side driver  206 , etc.) may operate at high speeds without external bypass capacitors. Additionally, by increasing the transfer conductance (i.e., transconductance) of power supplies  218  and  216 , transient driver currents may be compensated while reducing the need for external energy storage devices.  
         [0023]      FIG. 3  is one circuitry embodiment of low side driver power supply  216  that includes components for increasing transconductance of the supply. To increase the transconductance of power supply  216 , three transistors  302 ,  304  and  306  may be included in the power supply design. As described in detail below, due to the interaction of transistors  302 ,  304  and  306 , output impedance of power supply  216  may be decreased. By increasing the transconductance of power supply  36 , additional decoupling by large energy storage devices (e.g., bypass capacitors) may not be needed.  
         [0024]     To provide the +20 volts, power supply  216  may include a constant current source  308  that may be configured to develop a reference voltage V 1  across a resistor  310 . Resistor  310  may be connected to the source of a field-effect transistor (FET)  312 . Since the drain and gate of FET  312  are connected in this embodiment, the FET may function as an MOS diode for compensating threshold voltage variations in transistor  302 . A voltage V 2  may be present on the gate of FET  302 . Voltage V 2  may be approximately equivalent to voltage V 1  shifted by the gate-to-source voltage (V gs ) of FET  312 . Voltage V 2  may substantially cancel the variations in V T  and G M  of FET  302 .  
         [0025]     A quiescent output voltage (V out ) of power supply  216  may be approximately equivalent to V 1 . However, slight variations in V out  may be introduced due to different operating conditions and/or parameters respectively associated with FET  312  and FET  302 . In this embodiment, FET  302  may be configured as a common gate amplifier that may amplify the difference between voltage V out  and V 2 . To perform this function, FET  304  may operate as a load device for FET  302  and drive the gate of FET  306 , which may be configured as a common source amplifier. In this exemplary embodiment, three FETs  314 ,  316  and  318  may provide a voltage divider for biasing the gate of FET  304 . Power supply  216  may also include a FET  320  that may provide a relatively small bias current such that a small reverse output current or currents (e.g., due to leakage) may not substantially cause FET  302  to halt operations.  
         [0026]     When a load variation may be experienced, FET  302  and/or FET  306  may conduct current to the output of the power supply. By providing this additional current, the output conductance of power supply  216  may be increased. In particular, when the current drawn by low side driver  206  increases, the output voltage of low side power supply  216  may be reduced below a quiescent level. For example, the output voltage may be reduced by an amount ΔV. Based on this reduction, FET  302  conducts as indicated by current label I 1  and a voltage V 3  present at the gate of FET  306  may become a negative level. Due to V 3 , FET  306  may be biased “on” and current may conduct from the source to the drain of FET  306  as indicated by current label I 2 . Since FETs  302  and  306  may provide current (i.e., current I 1  and I 2 ) to the output of power supply  216 , the output conductance of power supply  36  may increase due to the additional current contributions. As illustrated, currents I 1  and I 2  may combine to produce current I 3 . Currents I 1  and I 2  may be provided with a relatively low output impedance since the transconductance of FET  306  may be amplified by the voltage gains of FET  302  and FET  304 .  
         [0027]     The increase in output conductance due to the contributions of FET  302  and  306  may be quantified from parameters associated with FETs  302 ,  304  and  306 . As mentioned above, conductance may increase when the output voltage of power supply  216  is reduced by ΔV, in which: 
 
 ΔV=V   2   −V   OUT .  (1) 
 
         [0028]     Using this voltage reduction ΔV: 
 
Δ I   1   =ΔVgm   302 ;  (2) 
 
         [0029]     Where gm 302  may be the transconductance of FET  302 ; 
 
Δ V   3   =ΔVgm   302   Rd   304 ;  (3) 
 
         [0030]     Where Rd 304  may be the drain resistance of FET  304 ;  
                 Δ   ⁢           ⁢     I   3       =       Δ   ⁢           ⁢     I   1       +     Δ   ⁢           ⁢     I   2           ;           (   4   )                   G   OUT     =       Δ   ⁢           ⁢     I   3         Δ   ⁢           ⁢     V   OUT           ;           (   5   )             
 
         [0031]     Where G out  is the output conductance of power supply  216 , and; 
 
 G   OUT   =gm   302 (1+ Rd   304   gm   306 ).  (6) 
 
         [0032]     Thus, as shown in equation (6), the output conductance of power supply  216  may be relatively large based on the transconductance of FET  302  and FET  306  and the drain resistance of FET  304 . By implementing FETs  302 ,  304  and  306 , external large capacitors may not be needed for handling relatively fast changing driver transient load currents. Additionally, this embodiment of power supply  216  may dissipate less power and may need less circuit board space compared to conventional n-channel designs.  
         [0033]      FIG. 4  is one circuitry embodiment of high side power supply  218  that provides a voltage level to high side driver  204  of H-bridge Controller Circuitry  104 . High side power supply  218  operates in a similar but complementary manner to low side power supply  216 . For example, three FETs may be incorporated into power supply  218  to compensate for transient load conditions. Some of these transient load conditions may cause the output voltage (e.g., +40 volts) of power supply  218  to increase above a desired level.  
         [0034]     In this embodiment, FETs  402 ,  404  and  406  may be included in power supply  218  to compensate for driver transient load conditions. This embodiment includes a constant current source  408  that may produce a voltage V 1  at a resistor  410  and a FET  412 . Voltage V 2  may be related to voltage V 1  by the gate-to-source voltage (V gs ) of FET  412 . As driver load conditions change, the output voltage may increase above a quiescent output level (e.g., +40 volts). By pulling the output V out  to a higher voltage (i.e., above +40 volts), the voltage difference between V out  and V 2  may bias FET  402  to conduct current as indicated by current label I 1 . FET  404 , which may function as a load device for FET  402 , may be biased by the voltage divider formed by FETs  414  and  416 . Due to the current I 1 , FET  406  may also be biased to conduct current as indicated with current label I 2 . By drawing currents I 1  and I 2 , the output voltage of power supply  218  may be reduced toward the quiescent level (e.g., +40 volts) of the supply. Similar to the power supply  216 , power supply  218  may include a FET  418  that may provide a standby current for FET  402 . Power supply  218  may also provide an output conductance as defined by equation (6), however, with reversed polarities.  
         [0035]     While the power supply embodiments shown in  FIG. 3  and  FIG. 4  (i.e., power supply  216  and power supply  218 ) incorporate field-effect transistors to compensate for transient load conditions, other types of switch devices may be implemented exclusively or in combination with field-effect transistors for output voltage compensation. For example, bipolar junction transistor (e.g., PNP BJTs, NPN BJTs, etc.) may be implemented in some power supply embodiments (with or without one or more FETs) for providing appropriate voltage levels to high and/or low side drivers that may drive H-bridge circuitry.  
         [0036]     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.

Technology Classification (CPC): 8