Abstract:
The present disclosure relates to an inkjet printing system that includes an inkjet printhead having a plurality of electrical contacts. The plurality of electrical contacts include address contacts and enable contacts for enabling drop generators and drive current contacts for providing drive current to enable drop generators for selectively ejecting ink therefrom. The printing system includes a printing device having a plurality of electrical contacts including address contacts, enable contacts and drive current contacts. The plurality of electrical contacts are configured to establish electrical contact with corresponding electrical contacts on the inkjet printhead upon insertion of the inkjet printhead into the printing device. The printing device provides periodic address signals and enable signals to the address and enable contacts one the printhead. In addition, the printing device selectively applies drive current to accomplish forming images on print media.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This is a Continuation of application Ser. No. 09/702,267, filed on Oct. 30, 2000, now U.S. Pat. No. 6,582,042 which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to inkjet printing devices, and more particularly to an inkjet printing device that includes a printhead portion that receives drop activation signals for selectively ejecting ink. 
     Inkjet printing systems frequently make use of an inkjet printhead mounted to a carriage which is moved back and forth across print media such as paper. As the printhead is moved across the print media, a control device selectively activates each of a plurality of drop generators within the printhead to eject or deposit ink droplets onto the print media to form images and text characters. An ink supply that is either carried with the printhead or remote from the printhead provides ink for replenishing the plurality of drop generators. 
     Individual drop generators are selectively activated by the use of an activation signal that is provided by the printing system to the printhead. In the case of thermal inkjet printing, each drop generator is activated by passing an electric current through a resistive element such as a resistor. In response to the electric current the resistor produces heat, that in turn, heats ink in a vaporization chamber adjacent the resistor. Once the ink reaches vaporization, a rapidly expanding vapor front forces ink within the vaporization chamber through an adjacent orifice or nozzle. Ink droplets ejected from the nozzles are deposited on print media to accomplish printing. 
     The electric current is frequently provided to individual resistors or drop generators by a switching device such as a field effect transistor (FET). The switching device is activated by a control signal that is provided to the control terminal of the switching device. Once activated the switching device enables the electric current to pass to the selected resistor. The electric current or drive current provided to each resistor is sometimes referred to as a drive current signal. The control signal for selectively activating the switching device associated with each resistor is sometimes referred to as an address signal. 
     In one previously used arrangement, a switching transistor is connected in series with each resistor. When active, the switching transistor allows a drive current to pass through each of the resistor and switching transistor. The resistor and switching transistor together form a drop generator. A plurality of these drop generators are then arranged in a logical two-dimensional array of drop generators having rows and columns. Each column of drop generators in the array are connected to a different source of drive current and with each drop generator within each column connected in a parallel connection between the source of drive current for that column. Each row of drop generators within the array is connected to a different address signal with each drop generator within each row connected to a common source of address signals for that row of drop generators. In this manner, any individual drop generator within the two-dimensional array of drop generators can be individually activated by activating the address signal corresponding to the drop generator of row and providing drive current from the source of drive current associated with the drop generator column. In this manner, the number of electrical interconnects required for the printhead is greatly reduced over providing drive and control signals for each individual drop generator associated with the printhead. 
     While the row and column addressing scheme previously discussed is capable of being implemented in relatively simple and relatively inexpensive technology tending to reduce printhead manufacturing costs, this technique suffers from the disadvantage of requiring relatively large number of bond pads for printheads having large numbers of drop generators. For printheads having in excess of three hundred drop generators, a number of bond pads tends to become a limiting factor when attempting to minimize the die size. 
     Another technique that has been previously been used makes use of transferring activation information to the printhead in a serial format. This drop generator activation information is rearranged using shift registers so that the proper drop generators can be activated. This technique, while greatly reducing the number of electrical interconnects, tends to require various logic functions as well as static memory elements. Printheads having various logic functions and memory elements require suitable technologies such as CMOS technology and tend to require a constant power supply. Printheads formed using CMOS technology tend to be more costly to manufacture than printheads using NMOS technology. The CMOS manufacturing process is a more complex manufacturing process than the NMOS manufacturing process that requires more masking steps that tend to increase the costs of the printhead. In addition, the requirement of a constant power supply tends to increase the cost of the printing device that must supply this constant power supply voltage to the printhead. 
     There is an ever present need for inkjet printheads that have fewer electrical interconnects between the printhead and the printing device thereby tending to reduce the overall costs of the printing system as well as the printhead itself. These printheads should be capable of being manufactured using a relatively inexpensive manufacturing technology that allows the printheads to be manufactured using high volume manufacturing techniques and have relatively low manufacturing costs. These printheads should allow information to be transferred between the printing device and the printhead in a reliable manner thereby allowing high print quality as well as reliable operation. Finally, these printheads should be capable of supporting large numbers of drop generators to provide printing systems that are capable of providing high print rates. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is an inkjet printing system that includes an inkjet printhead having a plurality of electrical contacts. The plurality of electrical contacts include address contacts and enable contacts for enabling drop generators and drive current contacts for providing drive current to enable drop generators for selectively ejecting ink therefrom. The printing system includes a printing device having a plurality of electrical contacts including address contacts, enable contacts and drive current contacts. The plurality of electrical contacts are configured to establish electrical contact with corresponding electrical contacts on the inkjet printhead upon insertion of the inkjet printhead into the printing device. The printing device provides periodic address signals and enable signals to the address and enable contacts one the printhead. In addition, the printing device selectively applies drive current to accomplish forming images on print media. 
     Another aspect of the present invention is an inkjet printhead responsive to enable and drive current signals for dispensing ink. The inkjet printhead includes an energy storage device for storing energy. Also included is an energy charging device responsive to a first enable signal for storing energy in the energy storage device. The inkjet printhead further includes an energy discharging device responsive to a second enable signal for discharging energy in the energy storage device. A drop generating device is included for dispensing ink from the inkjet printhead upon activation. The drop generating device is activated by a drive current signal active and energy stored in the energy storage device being greater than a threshold energy level. 
     Yet another aspect of the present invention is an inkjet printhead having a plurality of drop generators with each drop generator of the plurality of drop generators responsive to an activation signal and a drive current for selectively dispensing ink therefrom. The inkjet printhead includes a plurality of groups of drop generators for depositing ink on media Each of the plurality of groups of drop generators are capable of activation once over a printhead activation cycle. The printhead activation cycle is subdivided into a plurality of timeslots with each of the plurality of groups of drop generators having a corresponding timeslot associated therewith. The activation signal is active in the corresponding timeslot before drive current is provided. In addition, the activation signal is active for a duration that is less than a duration drive current is provided. Each drop generator within each group of drop generators is configured so that when activated the drop generator is active for the duration that drive current is provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a printing system of the present invention that incorporates an inkjet print cartridge of the present invention for accomplishing printing on print media shown in a top perspective view. 
     FIG. 2 depicts the inkjet print cartridge shown in FIG. 1 in isolation and viewed from a bottom perspective view. 
     FIG. 3 is a simplified block diagram of the printing system shown in FIG. 1 that includes a printer portion and a printhead portion. 
     FIG. 4 is a block diagram showing further detail of one preferred embodiment of a print control device associated with the printer portion and the printhead shown with  16  groups of drop generators. 
     FIG. 5 is a block diagram showing further detail of one group of drop generators having  26  individual drop generators. 
     FIG. 6 is a schematic diagram showing further detail of one preferred embodiment of one individual drop generator of the present invention. 
     FIG. 7 is a schematic diagram showing two individual drop generators for the printhead of the present invention shown in FIG.  5 . 
     FIG. 8 is a timing diagram for operating the printhead of the present invention shown in FIG.  4 . 
     FIG. 9 is an alternative timing diagram for operating the printhead of the present invention shown in FIG.  4 . 
     FIG. 10 is a detailed view of the timing for timeslots  1  and  2  of the timing diagram shown in FIG.  8 . 
     FIG. 11 is a detailed view of the timing for timeslots  1  and  2  of the alternative timing diagram shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a perspective view of one exemplary embodiment of an inkjet printing system  10  of the present invention shown with its cover open. The inkjet printing system  10  includes a printer portion  12  having at least one print cartridge  14  and  16  installed in a scanning carriage  18 . The printing portion  12  includes a media tray  20  for receiving media  22 . As the print media  22  is stepped through a print zone, the scanning carriage  18  moves the print cartridges  14  and  16  across the print media. The printer portion  12  selectively activates drop generators within a printhead portion (not shown) associated with each of the print cartridges  14  and  16  to deposit ink on the print media to thereby accomplish printing. 
     An important aspect of the present invention is a method for which the printer portion  12  transfers drop generator activation information to the print cartridges  14  and  16 . This drop generator activation information is used by the printhead portion to activate drop generators as the print cartridges  14  and  16  are moved relative to the print media Another aspect of the present invention is the printhead portion that makes use of the information provided by the printer portion  12 . The method and apparatus of the present invention allows information to be passed between the printer portion  12  and the printhead with relatively few interconnects thereby tending to reduce the size of the printhead. In addition the method and apparatus of the present invention allows the printhead to be implemented without requiring clocked storage elements or complex logic functions thereby reducing the manufacturing costs of the printhead. The method and apparatus of the present invention will be discussed in more detail with respect to FIGS. 3-11. 
     FIG. 2 depicts a bottom perspective view of one preferred embodiment of the print cartridge  14  shown in FIG.  1 . In the preferred embodiment, the cartridge  14  is a  3  color cartridge containing cyan, magenta, and yellow inks. In this preferred embodiment, a separate print cartridge  16  is provided for black ink. The present invention will herein be described with respect to this preferred embodiment by way of example only. There are numerous other configurations in which the method and apparatus of the present invention is also suitable. For example, the present invention is also suited to configurations wherein the printing system contains separate print cartridges for each color of ink used in printing. Alternatively, the present invention is applicable to printing systems wherein more than 4 ink colors are used such as in high-fidelity printing wherein  6  or more ink colors are used. Finally, the present invention is applicable to various types of print cartridges such as print cartridges which include an ink reservoir as shown in FIG. 2, or for print cartridges which are replenished with ink from a remote source of ink, either continuously or intermittently. 
     The ink cartridge  14  shown in FIG. 2 includes a printhead portion  24  that is responsive to activation signals from the printing system  12  for selectively depositing ink on media  22 . In the preferred embodiment, the printhead  24  is defined on a substrate such as silicon. The printhead  24  is mounted to a cartridge body  25 . The print cartridge  14  includes a plurality of electrical contacts  26  that are disposed and arranged on the cartridge body  25  so that when properly inserted into the scanning carriage, electrical contact is established between corresponding electrical contacts (not shown) associated with the printer portion  12 . Each of the electrical contacts  26  is electrically connected to the printhead  24  by each of a plurality of electrical conductors (not shown). In this manner, activation signals from the printer portion  12  are provided to the inkjet printhead  24 . 
     In the preferred embodiment the electrical contacts  26  are defined in a flexible circuit  28 . The flexible circuit  28  includes an insulating material such as polyimide and a conductive material such as copper. Conductors are defined within the flexible circuit to electrically connect each of the electrical contacts  26  to electrical contacts defined on the printhead  24 . The printhead  24  is mounted and electrically connected to the flexible circuit  28  using a suitable technique such as tape automated bonding CMAB). 
     In the exemplary embodiment shown in FIG. 2, the print cartridge is a 3 color cartridge containing yellow, magenta, and cyan inks within a corresponding reservoir portion. The printhead  24  includes drop ejection portions  30 ,  32  and  34  for ejecting ink corresponding, respectively, to yellow, magenta, and cyan inks. The electrical contacts  26  include electrical contacts associated with activation signals for each of the yellow, magenta, and cyan drop generators  30 ,  32 ,  34 , respectively. 
     In the preferred embodiment, the black ink cartridge  16  shown in FIG. 1 is similar to the color cartridge  14  shown in FIG. 2 except the black cartridge makes use of two drop ejection portions instead of three shown on the color cartridge  14 . The method and apparatus of the present invention will be discussed herein with respect to the black cartridge  16 . However, the method and apparatus of the present invention is applicable to the color cartridge  14  as well. 
     FIG. 3 depicts a simplified electrical block diagram of the printer portion  12  and one of the print cartridges  16 . The printer portion  12  includes a print control device  36 , a media transport device  38  and a carriage transport device  40 . The print control device  36  provides control signals to the media transport device  38  to pass the media  22  through a print zone whereupon ink is deposited on the print media  22 . In addition, the print control device  36  provides control signals for selectively moving the scanning carriage  18  across the media  22 , thereby defining a print zone. As the media  22  is stepped past the printhead  24  or through the print zone the scanning carriage  18  is scanned across the print media  22 . While the printhead  24  is scanned the print control device  36  provides activation signals to the printhead  24  to selectively deposit ink on print media to accomplish printing. Although, the printing system  10  is described herein as having the printhead  24  disposed in a scanning carriage there are other printing system  10  arrangements as well. These other arrangements involve other arrangements of achieving relative movement between the printhead and media such as having a fixed printhead portion and moving the media past the printhead or having fixed media and moving the printhead past the fixed media. 
     FIG. 3 is simplified to show only a single print cartridge  16 . In general, the print control device  36  is electrically connected to each of the print cartridges  14  and  16 . The print control device  36  provides activation signals to selectively deposit ink corresponding to each of the ink colors to be printed. 
     FIG. 4 depicts a simplified electrical block diagram showing greater detail of the print control device  36  within the printer portion  12  and the printhead  24  within the print cartridge  16 . The print control device  36  includes a source of drive current, an address generator, and an enable generator. The source of drive current, address generator and enable generator provide drive current, address and enable signals under control of the control device or controller  36  to the printhead  24  for selectively activating each of a plurality of drop generators associated therewith. 
     In the preferred embodiment, the source of drive current provides 16 separate drive current signals designated P ( 1 - 16 ). Each drive current signal provides sufficient energy per unit time to activate the drop generator to eject ink. In the preferred embodiment, the address generator provides 13 separate address signals designated A( 1 - 13 ) for selecting a group of drop generators. In this preferred embodiment the address signals are logic signals. Finally, in the preferred embodiment, the enable generator provides 2 enable signals designated E ( 1 - 2 ) for selecting a subgroup of drop generators from the selected group of drop generators. The selected subgroup of drop generators are activated if drive current provided by the source of drive current is supplied. Further detail of the drive signals, address signals and enable signals will be discussed with respect to FIGS. 9-11. 
     The printhead  24  shown in FIG. 4 includes a plurality of groups of drop generators with each group of drop generators connected to a different source of drive current. In the preferred embodiment, the printhead  24  includes 16 groups of drop generators. The first group of drop generators is connected to the source of drive current labeled P( 1 ), the second group of drop generators are each connected to the source of drive current designated P( 2 ), the third group of drop generators is connected to the source of drive current designated P( 3 ), and so on with the sixteenth group of drop generators each connected to the source of drive current designated P( 16 ). 
     Each of the groups of drop generators shown in FIG. 4 are connected to each of the address signals designated A( 1 - 13 ) provided by the address generator on the print control device  36 . In addition, each of the groups of drop generators are connected to the two enable signals designated E( 1 - 2 ) provided by the address generator on the print control device  36 . Greater detail of each of the individual groups of drop generators designated will now be discussed with respect to FIG.  5 . 
     FIG. 5 is a block diagram representing a single group of drop generators from the plurality of groups of drop generators shown in FIG.  4 . In the preferred embodiment, the single group of drop generators shown in FIG. 5 is a group of  26  individual drop generators each connected to a common source of drive current. The group of drop generators shown in FIG. 5 are all connected to the common source of drive current designated P( 1 ) of FIG.  4 . 
     The individual drop generators within the group of drop generators are organized in drop generator pairs with each pair of drop generators connected to a different source of address signals. For the embodiment shown in FIG. 5, the first pair of drop generators are connected to a source of address signals designated A( 1 ), the second pair of drop generators are connected to a second source of address signals designated A( 2 ), the third pair of drop generators are connected to a source of address signals designated A( 3 ) and so on with the thirteenth pair of drop generators connected to the thirteenth source of address signals designated A( 13 ). 
     Each of the  26  individual drop generators shown in FIG. 5 are also connected to the source of enable signals. In the preferred embodiment, the source of enable signals is a pair of enable signals designated E( 1 - 2 ). 
     The remaining groups of drop generators shown in FIG. 4 that are connected to the remaining sources of drive current designated P( 2 ) through P( 16 ) are connected in a manner similar to the first group of drop generators shown in FIG.  5 . Each of the remaining groups of drop generators are connected to a different source of drive current as designated in FIG. 4 instead of the source of drop current P( 1 ) shown in FIG.  5 . Greater detail of each individual drop generator shown in FIG. 5 will now be discussed with respect to FIG.  6 . 
     FIG. 6 shows one preferred embodiment of an individual drop generator designated  42 . The drop generator  42  represents one individual drop generator shown in FIG.  5 . As shown in FIG. 5 two individual drop generators  42  make up a pair of drop generators  42  that are each connected to a common source of address signals. The individual drop generator shown in FIG. 6 represents one of the pair of drop generators  42  connected to address source I designated A( 1 ) of FIG.  5 . All sources of signals such as address signals A( 1 ) and enable signals E( 1 - 2 ) discussed with respect to FIGS. 6 and 7 are signals that are provided between the corresponding source of signals and the common reference point  46 . In addition, the source of drive current is provided between the corresponding source of drive current designated P( 1 ) and the common reference point  46 . 
     The drop generator  42  includes a heating element  44  connected between the source of drive current. For the particular drop generator  42  shown in FIG. 6 the source of drive current is designated P( 1 ). The heating element  44  is connected in series with a switching device  48  between the source of drive current P( 1 ) and the common reference point  46 . The switching device  48  includes a pair of controlled terminals connected between the heating element  44  and the common reference point  46 . Also included with the switching device  48  is a control terminal for controlling the controlled terminals. The switching device  48  is responsive to activation signals at the control terminal for selectively allowing current to pass between the pair of controlled terminals. In this manner, activation of the control terminals allows drive current from the source of drive current designated P( 1 ) to pass through the heating element  44  thereby producing heat energy that is sufficient to eject ink from the printhead  24 . 
     In one preferred embodiment, the heating element  44  is a resistive heating element and the switching device  48  is a field effect transistor (FET) such as an NMOS transistor. 
     The drop generator  42  further includes a second switching device  50  and a third switching device  52  for controlling activation of the control terminal of the switching device  48 . The second switching device has a pair of controlled terminals connected between a source of address signals and the control terminal of switching device  48 . The third switching device  52  is connected between the control terminal of switching device  48  and the common reference point  46 . Each of the second and third switching devices  50  and  52 , respectively, selectively control the activation of the switching device  48 . 
     The activation of switching device  48  is based on each of the address signal and enable signal. For the particular drop generator  42  shown in FIG. 6 the address signal is represented by A( 1 ), the first enable signal represented by E( 1 ) and a second enable signal represented by E( 2 ). The first enable signal E( 1 ) is connected to the control terminal of the second switching device  50 . The second enable signal represented by E( 2 ) is connected to the control terminal of the third switching device  52 . By controlling the first and second enable signals, E( 1 - 2 ), and the address signal, A( 1 ), the switching device  48  is selectively activated to conduct current through the heating element  44  if drive current is present from the source of drive source P( 1 ). Similarly, the switching device  48  is inactivated to prevent current from being conducted through the heating resistor  44  even if the source of drive current P( 1 ) is active. 
     The switching device  48  is activated by the activation of the second switching device  50  and the presence of an active address signal at the source of address signals, A( 1 ). In the preferred embodiment where the second switching device is a field effect transistor (FET) the controlled terminals associated with the second switching device are source and drain terminals. The drain terminal is connected to the source of address signals A( 1 ) and the source terminal is connected to the controlled terminal of the first switching device  48 . The control terminal for the FET transistor switching device  50  is a gate terminal. When the gate terminal, connected to the first enable signal E( 1 ), is sufficiently positive relative to the source terminal and the source of address signals, A( 1 ), provides a voltage at the drain terminal that is greater than the voltage at the source terminal then the second switching device  50  is activated. 
     The second switching device, if active, provides current from the source of address signals A( 1 ) to the control terminal or gate of the switching device  48 . This current, if sufficient, activates the switching device  48 . The switching device  48 , in the preferred embodiment, is a FET transistor having a drain and source as the controlled terminals with the drain connected to the heating element  44  and the source connected to the common reference terminal  46 . 
     In the preferred embodiment, the switching device  48  has a gate capacitance between the gate and source terminals. Because this switching device  48  is relatively large to conduct relatively large currents through the heating device  44 , then the gate to source capacitance associated with the switching device  48  tends to be relatively large. Therefore, to enable or activate the switching device  48 , the gate or control terminal must be charged sufficiently so that the switching device  48  is activated to conduct between the source and drain. The control terminal is charged by the source of address signals A( 1 ) if the second switching device  50  is active. The source of address signals A( 1 ) provides current to charge the gate to source capacitance of the switching device  48 . It is important that the third switching device  52  be inactive when the switching device  48  is active to prevent a low resistance path from being formed between the source of address signals A( 1 ) and the common reference terminal  46 . Therefore, the enable signal E( 2 ) is inactive while the switching device  48  is active or conducting. 
     The switching device  48  is inactivated by activating the third switching device  52  to reduce the gate to source voltage sufficiently to inactivate the switching device  48 . The third switching device  52  in the preferred embodiment is a FET transistor having drain and source as the controlled terminals with the drain connected to the control terminal of switching device  48 . The control terminal is a gate terminal that is connected to the second source of enable signals E( 2 ). The third switching device  52  is activated by activation of the second enable signal E( 2 ) that provides a voltage at the gate that is sufficiently large relative to a voltage at the source of the third switching device  52 . Activation of the third switching device  52  causes the controlled terminals or drain and source terminals to conduct thereby reducing a voltage between the control terminal or gate terminal of the switching device  48  and the source terminal of the switching device  48 . By sufficiently reducing the voltage between the gate terminal and the source terminal of the switching device  48  the switching device  48  is prevented from being partially turned on by capacitive coupling. 
     While the third switching device  52  is active, the second switching  50  is inactive to prevent sinking large amounts of current from the source of address signals, A( 1 ), to the common reference terminal  46 . The operation of the individual drop generator  42  will be discussed in more detail with respect to the timing diagrams shown in FIGS. 8 through 11. 
     FIG. 7 shows greater detail of a pair of drop generators that are formed by the drop generator designated  42  and a drop generator designated  42 ′. Each of the drop generators  42  and  42 ′ that form the pair of drop generators are identical to the drop generator  42  discussed previously with respect to FIG.  6 . The pair of drop generators are each connected to a source of address signals represented by A( 1 ) shown in FIG.  5 . Each of the drop generators  42  and  42 ′ are connected to a common source of drive current P( 1 ) and common source of address signals A( 1 ). However, the first and second enable signals E( 1 ) and E( 2 ), respectively, are connected differently in drop generator  42 ′ from drop generator  42 . In drop generator  42 ′, the first enable signal E( 1 ) is connected to the gate or control terminal of the third switching device  52 ′ in contrast to drop generator  42  in which the first enable signal gate or control terminal of the second switching device  50 . Similarly, the second enable signal E( 2 ) is connected to the gate or control terminal of the second switching device  50 ′ in the drop generator  42 ′ in contrast to the drop generator  42  where the second enable signal E( 2 ) is connected to the gate or control terminal of the third switching device  52 . 
     The connection of the first and second enable signals E 1  and E 2  for the pair of drop generators  42  and  42 ′ ensures that only a single drop generator of the pair of drop generators will be activated at a given time. As will be discussed later, it is important that within the group of drop generators that are connected to a common source of drive current that no more than one of these drop generators is active at the same time. The drop generators that are connected to a common source of drive current tend to be positioned near each other on the printhead. Therefore, by ensuring that no more than one of the drop generators that are connected to a common source of drive current of these is active at the same time tends to prevent fluidic crosstalk between these proximately positioned drop generators. 
     In the preferred embodiment, each of the pairs of drop generators shown in FIG. 5 are connected in a manner similar to the pair of drop generators shown in FIG.  7 . In addition, each of the groups of drop generators connected to a common source of drive current shown in FIG. 4 are connected in a manner similar to the group of drop generators shown in FIG.  5 . 
     FIG. 8 is a timing diagram illustrating the operation of printhead  24 . The printhead  24  has a cycle time or period of time in which each of the drop generators on the printhead  24  can be activated. This period of time is represented by a time T shown in FIG.  8 . The time T can be divided into  29  internals of time with each interval having the same duration. These intervals of time are presented by time slots  1  through  29 . Each of the first  26  time slots represents a period in which a group of drop generators can be activated if the image to be printed so requires. Time slots  27 ,  28  and  29  represent intervals of time during a printhead cycle in which no drop generators are activated. The time slots  27 ,  28 , and  29  are used by the printing system  10  to perform a variety of functions such as resynchronize the carriage  18  position and drop generator activation data and transfer activation data from the printer portion  12  to the printhead  24 , to name a couple. 
     The  13  different sources of address signals represented by A( 1 ) through A( 13 ) are each shown. In addition, each of the first and second enable signals represented by E( 1 ) and E( 2 ) are also shown. Finally, each of the sources of drive current P ( 1 - 16 ) are also shown, grouped together. It can be seen from FIG. 8 that the address signals are each activated periodically with the period of activation for each address signal being equal to the cycle time T of the printhead  24 . In addition, no more than one address signal is active at the same time. Each address signal is active during two consecutive time slots. 
     Each of the enable signals E( 1 ) and E( 2 ) are periodic signals having a period that is equal to two time slots. The enable signals E( 1 ) and E( 2 ) each have a duty cycle that is less than or equal to 50%. Each of the enable signals are out of phase with each other so that only one of enable signal E( 1 ) or E( 2 ) are active at the same time. 
     In operation, repeating patterns of address signals provided by each of the  13  sources of address signals A( 1 - 13 ) are provided to the printhead  24  by the print control device  36 . In addition, repeating patterns of enable signals for the first and second enable signals, E( 1 ) and E( 2 ), respectively, are also provided by the print control device  36  to the printhead  24 . Both the address and enable signals are generated independent of the image description or image to be printed. Each of the  16  sources of drive current designated P( 1 - 16 ) are selectively provided during each of the  26  time slots for each complete cycle for the inkjet printhead  24 . The source of drive current P( 1 - 16 ) is selectively applied based on the image description or the image to be printed. During the first time slot, the sources of drive current P( 1 - 16 ) may all be active, none of them active or any number of them active, depending upon the image to be printed. Similarly, for time slots  2 - 26 , each of the sources of drive current P( 1 - 16 ) are individually selectively activated as required by the print control device  36  to form the image to be printed. 
     FIG. 9 is a preferred timing diagram for each of the sources of drive current P( 1 - 16 ), sources of address signals A( 1 - 13 ) and enable signals E( 1 - 2 ) for the printhead  24  of the present invention. The timing in FIG. 9 is similar to the timing of FIG. 8 except that each source of address signals A( 1 - 13 ) instead of remaining active over the entire two consecutive time slots shown in FIG. 8, each address is active for only a portion of each of the two time slots shown in FIG.  9 . In this preferred embodiment, each of the address signals A( 1 - 13 ) are active at the beginning of each time slot the address signal is active. In addition, the duty cycle of each of the first and second enable signals reduced from the nearly 50% duty cycle shown in FIG.  8 . Further detail of the timing of the address enable and drive current will now be discussed with respect to FIGS. 10 and 11. 
     FIG. 10 shows greater detail of time slots  1  and  2  for the timing diagram of described in FIG.  8 . Because the only active address signal during time slot  1  and  2  is A( 1 ) only the address signal A( 1 ) need be shown in FIG.  10 . As discussed previously, it is important that the first and second enable signals, E( 1 ) and E( 2 ) respectively, not be active at the same time to prevent providing a low resistance path to the common reference point  46  thereby sinking current from the source of address signals A( 1 - 13 ). Therefore, the duty cycle of each of the first and second enable signals, E( 1 ) and E( 2 ) respectively, should be less than 50%. In FIG. 10 the time interval labeled TE between the transition from active to inactive for the first enable signal E( 1 ) and the transition from inactive to active for the second enable signal E( 2 ) should be greater than zero. 
     The enable signal should be active before drive current is provided by the source of drive current to ensure that the gate of capacitance of the switching transistor  48  is sufficiently charged to activate the drive transistor  48 . The time interval labeled T S  represents the time between the first enable E( 1 ) active and the application of the drive current by the sources of drive current P( 1 - 16 ). A similar time interval is required for the time between the second enable E( 2 ) active and the application of the drive current by the sources of drive current P( 1 - 16 ). 
     The enable signal E( 1 ) should remain active for a period of time after the source of drive current P( 1 - 16 ) transitions from active to inactive as designated T H . This period of time T H  referred to as hold time is sufficient to ensure that drive current is not present at the switching device  48  when the switching device  48  is inactivated. Inactivating the switching device  48  while the switching device  48  is conducting current between the controlled terminals can damage the switching device  48 . The hold time T H  provides margin to ensure the switching device  48  is not damaged. The duration of the drive current signal P( 1 - 16 ) is represented by time interval labeled TD. The duration of drive current signal P( 1 - 16 ) is selected to be sufficient to provide drive energy to the heating element  44  for optimum drop formation. 
     FIG. 11 shows further detail of the preferred timing for time slots  1  and  2  for the timing diagram of FIG.  9 . As shown in FIG. 11 for time slot  1  the source of address signals A( 1 ) and the source of enable signals E( 1 ) do not remain active the entire duration that the source of drive current remains active. Once the gate capacitance of the switching transistor  48  and  48 ′ shown in FIG. 7 is charged, the transistor  48  and  48 ′ remain conducting the remaining duration that the source of drive current remains active. In this manner, the gate capacitance of the switching device  48  and  48 ′ acts as a storage device or memory device that retains an activated state. The switching device  48  and  48 ′ are selected to have sufficient capacitance so that charge stored within this capacitance remains beyond a threshold amount to keep the switching device  48  and  48 ′ conducting while the drive current signal is active. The source of drive signals designated P( 1 - 16 ) then provides the drive energy that is necessary for optimum drop formation. 
     Similar to FIG. 10 the time interval labeled T S  represents the time between the first enable E( 1 ) active and the application of the drive current by the sources of drive current P( 1 - 16 ). An interval of time labeled T AH  represents a hold time the source of address signals A( 1 ) must remain active after the first enable signal E( 1 ) is inactive to ensure the gate capacitance for transistor  48 ′ is in the proper state. If the source of address signals were to change state before the first enable signal E( 1 ) signal becomes inactive the wrong state of charge can exist at the gate of transistors  48  and  48 ′. Therefore, it is important that the time interval labeled T AH  be greater than 0. An interval of time labeled T EH  represents a hold time the second enable signal E( 2 ) must be active after the source of drive current P( 1 - 16 ) becomes active. During the time interval transistor  52  in FIG. 7 is activated by the second enable signal E( 2 ) to discharge the gate capacitance of transistor  48 . If this duration is not sufficiently long to discharge the gate of transistor  48  the heating element  44  may improperly be activated or partially activated. 
     Operation of the inkjet printhead  24  using the preferred timing shown FIG. 11 has important performance advantages over the use of the timing shown in FIG. 10. A minimum time required for each drop generator  42  activation for the timing shown in FIG. 10, is equal to the sum of time intervals T S , T D , T E  and T H . In contrast, the timing shown in FIG. 11 has a minimum time that is required for each drop generator  42  activation that is equal to the sum of time intervals T S , and T D . Because T D  and T S  is the same for each of the timing diagrams, the minimum time required for activation of a drop generator  42  is less in FIG. 11 than in FIG.  10 . Both the address hold time T AH  and the enable hold time T EH  do not contribute to the minimum time interval for drop generator  42  activation in the preferred timing shown in FIG. 11 thereby allowing each time slot to be a smaller time interval than in FIG.  10 . Reduction of the time interval required for each time slot reduces the cycle period designated T in FIGS. 8 and 9 thereby increasing the printing rate for the printhead  24 . 
     The method and apparatus of the present invention allows 416 individual drop generators to be individually activated using 13 address signals, two enable signals, and 16 sources of drive current. In contrast, the use of previously used techniques whereby an array of drop generators having 16 columns and 26 rows would require 26 individual addresses to individually select each row with each column being selected by each source of drive current. The present invention provides significantly fewer electrical interconnects to address the same number of drop generators. The reduction of electrical interconnects reduces the size of the printhead  24  thereby significantly reducing the costs of the printhead  24 . 
     Each individual drop generator  42  as shown in FIG. 6 does not require a constant power supply or bias circuit but instead relies on the input signals such as address, source of drive current, and enable signals to supply power or activate the drop generator  42 . As discussed previously with respect to the timing of the signals, it is important that these signals be applied in the proper sequence in order to have proper operation of the drop generator  42 . Because the drop generator  42  of the present invention does not require constant power, the drop generator  42  can be implemented in relatively simple technology such as NMOS which requires fewer manufacturing steps then more complex technology such as CMOS. Use of a technology that has lower manufacturing costs further reduces the costs of the printhead  24 . Finally, the use of fewer electrical interconnects between the printer portion  36  and the printhead  24  tends to reduce the costs of the printer portion  36  as well as increase the reliability of the printing system  10 . 
     Although the present invention has been described in terms of a preferred embodiment that makes use of 13 address signals, two enable signals, and 16 sources of drive current to selectively activate 416 individual drop generators other arrangements are also contemplated. For example, the present invention is suitable for selectively activating different numbers of individual drop generators. The selective activation of different numbers of individual nozzles may require different numbers of one or more of the address signals, enable signals, and sources of drive current to properly control different numbers of drop generators. In addition, there are other arrangements of address signals, enable signals; and sources of drive current to control the same number of drop generators as well.