the following description is of the best mode presently contemplated for carrying out the invention . this description is not to be taken in a limiting sense , but is made merely for the purpose of describing the general principles of the invention . the scope of the invention should be determined with reference to the claims . the dbs system of the present invention includes a cranium mountable pulse generator , support for two electrode cables supporting bilateral brain stimulation , electrodes specifically designed for the small structures required for the dbs application , and an electrode fixation system guaranteeing reliable electrode and lead wire position once implanted . a dbs system 10 made in accordance with the invention is illustrated in fig1 . the dbs system 10 includes an implantable pulse generator ( ipg ) 20 adapted to be implanted directly in or on the cranium 16 of a patient . at least one lead 30 , having a plurality of electrodes 32 thereon , is attached to the ipg 20 via a suitable connector 22 . up to two separate leads 30 may be attached to the ipg 20 . hence , fig1 shows ( in phantom lines ) a second lead 30 ′, having electrodes 32 ′ thereon , also attached to the ipg 20 . each lead includes at least two electrodes 32 , and may include as many as sixteen electrodes 32 . a preferred ipg 20 has four channels and can drive up to sixteen electrodes . the ipg 20 includes a rechargeable battery . the battery is recharged , as required , from an external battery charging system ( ebcs ) 40 , typically through an inductive link 42 . the ipg 20 , as explained more fully below , includes a processor and other electronic circuitry that allows it to generate stimulus pulses that are applied to the patient through the electrodes 32 in accordance with a stored program . the ipg 20 is programmed and tested through a hand held programmer ( hhp ) 50 ; a clinician programming system ( cps ) 60 that uses an hhp , or equivalent , to relay information ; or a manufacturing and diagnostic system ( mds ) 70 . the hhp 50 may be coupled to the ipg 20 via a suitable wireless link 44 . similarly , the mds 70 may be coupled to the ipg 20 via another wireless link 45 . any type of wireless link may be used , e . g ., a radio frequency ( rf ) link , or an infrared link . the cps 60 , which is coupled to the ipg 20 by way of the hhp 50 , may also be coupled to the hhp 50 via a wireless link 46 . the link 46 , in one preferred embodiment is an infrared link . likewise , the mds 70 may be coupled to the hhp via another wireless link 47 , e . g ., a second infrared link . other types of telecommunicative wireless links , other than rf or infrared may also be used for this purpose . through these links , the cps 60 , for example , may be coupled through the hhp 50 to the ipg 20 for programming or diagnostic purposes . the mds may also be coupled to the ipg 20 , either directly through the rf link 45 , or indirectly through the ir link 47 with the hhp 50 . turning next to fig2 , a block diagram of the dbs system 10 is illustrated , including the various elements within each of the main sub - systems of the dbs system . the subsystems of the dbs system 10 include an implantable pulse generator ( ipg ) 20 , a hand - held programmer ( hhp ) 50 , a clinician &# 39 ; s programming system ( cps ) 60 , a manufacturing and diagnostic system ( mds ) 70 , and an external battery charging system ( ecbs ) 40 . as seen in fig2 , the ipg 20 includes various elements , including a microprocessor 21 , ipg firmware 22 , a sram memory 23 ( which sram memory is optional , and may not be needed in some embodiments ), a seerom memory 24 , an analog ipg pulse generator integrated circuit ( ic ) 25 ( which analog pulse generator circuit 25 functions as the output circuit of the ipg ), a digital ipg pulse generator ic 26 , a rechargeable battery 27 , a battery charging system and telemetry circuit 28 , and an rf telemetry circuit 29 . the microprocessor 21 , in the preferred embodiment , comprises a 16 bit microprocessor and associated external controller based upon the vautomation 8086 processor , or equivalent . advantageously , this processor 21 is a flexible 16 bit processor that has been around for years and was the processor used in the ibm pc , thus many development tools are available for both software and hardware design for this device . the general performance - based features for the core and the additional peripheral devices in the mircoprocessor ic 21 are summarized as follows : 1 . core : equivalent to intel 8086 from vautomation , or equivalent . 2 . operating voltage : 2 . 2 - 3 . 5v 3 . oscillator — 1 . 048 mhz crystal controlled oscillator , under 1 ua current consumption , 2 . 2 - 3 . 5v supply 4 . address bus : 20 bit , non - multiplexed 5 . data bus : 16 bit , non - multiplexed , supports multiplexed with cpu_ale signal 6 . power consumption : 300 ua @ 1 mhz main crystal frequency 7 . memory : rom — 1 kbyte mask rom , containing bootstrap and initialization routines ; sram — 16 kbyte , used for program and data space 8 . external memory : provision for powering and reading from and writing to atmel seeprom for operating system and initial parameter storage ; provision for none , 256 or 512 kbytes external sram 9 . analog to digital converter : 12 bit , 4 channel signal multiplexer , 3 differential , 1 single - ended input signals , vcc measurement — warm - up in 1 ms , conversion time : & lt ; 50 clocks ( successive approximation ), programmable range and offset , external vrh and vrl , separate vdd connection 10 . synchronous serial interfaces ( 2 )— clock and data in , clock and data out , handshake in and out 11 . piezo buzzer control — 7 bit tone register , bipolar or monopolar drive , 35568 hz base block , tone is clock divided by 7 bit value in register , 8 th bit is on / off control 12 . interrupt control — 3 external interrupt request lines , high true 13 . invalid address detection non - maskable interrupt 14 . external i / o device select , low true 15 . rf telemetry : qfast modulation method with demodulator and rf mixer circuitry , power control for external rf circuitry , antenna tuning control : 4 bits , device id registers : 24 bit , timing control for automatic receive , with clock pulse stealer circuitry for time base adjustment , data rate 512 bits per second to 8192 bits per second 16 . wakeup timers : timer 1 - 10 bit up - counter , 1 hz drive , hirq on compare to value , then reset and up count again , range of programmable values is 3 sec to 1026 seconds ; timer 2 - 12 bit up - counter , 8 hz drive , hirq on compare to value , then reset and up count again ; timer 3 - 12 bit up - counter , 1024 hz drive , hirq on compare to value , then reset and count again 17 . one - minute counter — modulo 60 counter driven by 1 hz and hirq generator 18 . time of day registers 19 . watchdog monitor — wakeup timer 1 interrupt signal is monitored and if two successive hirq3 signals are detected without proper watchdog supervision by the main processor then a system reset is asserted . 20 . lcd clock — clock line for external lcd display ( to be used in hhp ) 21 . test pins for system control bus visibility and debug 22 . general purpose i / o used for pump control , but useful for other functions 23 . power on clear reset circuitry the rf telemetry circuit 29 utilized within the ipg 20 , in one preferred embodiment , is based on qfast technology . qfast stands for “ quadrature fast acquisition spread spectrum technique ”, and represents a known and viable approach for modulating and demodulating data . the qfast rf telemetry method is further disclosed in u . s . pat . no . 5 , 559 , 828 , incorporated herein by reference . the qfast methodology utilizes an i / q modulation and demodulation scheme that synchronously encodes clock and data onto a carrier signal of a suitable frequency , e . g ., 262 khz . the rf receive mixer and demodulator sections are implemented almost entirely on the processor ic with only external receive amplifier circuitry and an antenna required to supplement the circuit . a method of tuning the antenna due to center frequency shifts upon laser welding the enclosure around the processor hybrid is implemented under software control . pre - weld tuning is accomplished by the use of binary capacitors ( capacitor chip arrays which are wire bonded during fabrication and tuned by testing and creating wire bonds as needed ). the rf carrier is derived from the processor system clock . in one embodiment , the system clock operates at 1 . 000 mhz . other frequency ranges may be used , as needed . the data rate is adjustable by register control over a suitable range , e . g ., from 512 to 4096 bits per second , and the range of the link at 4 kb / s ( kilobits / second ) through an 8 mil titanium enclosure is greater than 40 inches . other components or elements within the ipg 20 may be conventional or as known in the art . still with reference to fig2 , the hand held programmer 50 is used by the patient to control the operation of the dbs implantable pulse generator ( ipg ). the hhp functions as a small pager - like device which is designed to control the ipg . the hhp , in one embodiment , uses a 16 bit microprocessor 51 as its main controller . this microprocessor 51 may be the same as the microprocessor 21 , used within the ipg 20 , and thus has all of the benefits and features described previously . the following is a summary of the features of the hhp 50 : 1 . package — central electronics volume is sealed against moisture ingress . battery compartment is moisture resistant . esd protection — internal surfaces treated for esd protection . size — 3 . 5 ″ l × 2 . 6 ″ w × 0 . 65 ″ t ; shape — landscape pager . 2 . lcd : pixel area — 128 columns by 55 rows ; icon area — above pixel area — time of day , month , date , activity icon , battery warning , alarm warning , reservoir volume ( battery charge ); interface — spi , iic or 8 bit parallel — spi implemented to ssi of asic ; programming — bit mapped graphics instruction set ; contrast — hardware and software command ; power consumption & lt ; 20 ua icon , & lt ; 500 ua pixel area on . 3 . keyboard : number of keys 5 , one hidden ; action , any key can cause interrupt request , maskable ; seal / environmental — sealed to prevent moisture ingress , esd shielded and debounced ; reset — hardware reset if all five keys pressed together 4 . vibrator — a pager type vibrator motor is available for non - audible alerts to the user — power consumption —& lt ; 60 ma , control — single bit control 5 . audio transducer — performance —& gt ; 75 db spl output at 2 khz ; power consumption & lt ; 10 ma , control — 7 bit register for tone control , 1 bit for on / off 6 . irda port — 115 kbit / s fixed data rate , irda 1 . 2 low power standard compliant . can be powered down , as can uart . irda port receive line can be powered independently to see if external device needs attention even when uart is off . 7 . batteries and up - conversion — main battery : lithium primary ; expected battery life — preferably more than 60 weeks , but at least 2 months at average current of 1 ma . 8 . processor : 8086 core asic — see specification for processor ic and vautomation specification memory : 1 kbyte boot rom , 16 kbyte internal sram , 1 mbyte external sram memory space , bank decoded into two pages , two 4 mbit devices , accessible byte or wordwise ; 512k 9 . external seeprom — four 64 kbyte devices at address 0 , 1 , 2 , 3 . the hhp 50 is designed to support multiple languages through the use of its graphics lcd and to display continuously basic status information about the implanted device and its own operation . the hhp 50 can perform rf telemetry to the ipg at the specifications mentioned above , as well as communicate over an irda 1 . 2 compatible infrared cable - less data link at 115 kbaud over a 30 cm range . this range can be extended with the use of a commercially available irda 1 . 2 compliant serial port 8 foot expander which plugs into the 9 pin sub - d connector found on personal computers and terminates with an irda transceiver . as can be seen in fig2 , the dbs system 10 includes four major functional blocks : the implanted pulse generator ( ipg ) 20 ; the hand - held programmer ( hhp ) 50 ; the external battery charging system ( ebcs ) 40 ; and the clinician &# 39 ; s programming system ( cps ) 60 . as previously indicated , the ipg 20 contains a 16 bit microprocessor 21 , memory 23 and 24 , a rechargeable battery 27 and custom pulse generation circuitry 25 and 26 . communication to the ipg 20 is via rf link 44 or other links 42 or 45 . the hhp 50 takes the form of a small pager - like device , with an lcd graphics display and a simple and direct user interface and keyboard . the hhp 50 is able to communicate with the ipg 20 over a comfortable distance , e . g ., up to 2 feet away , allowing the patient and clinician alike simple and efficient control of the ipg . the cps 60 is used by the clinician to fit the ipg 20 and electrodes 32 to the patient , and to record and document all stimulation settings . the cps 60 communicates to the hhp 50 using an infrared wireless link 46 , a standard in the computer industry . the hhp 50 communicates to the ipg 20 over an rf link 44 . secure communications without error are provided by utilizing a 24 bit identification code for all components in the system along with error detection codes embedded in all data packets submitted by any device in the system . the hhp 50 , in one embodiment , utilizes a label and membrane keypad to adapt to dbs applications . software applicable to dbs is also used . the hhp 50 represents a general - purpose 8086 - based product platform . such platform is extremely flexible , yet meets the needs of small weight and size , rugged environmental protections and ease of use for the dbs application . the packaging of the implanted pulse generator ( ipg ) 20 and its lead ( s ) 30 and electrodes 32 and electrode leadwire fixation system represent an important part of the system . a distally - located pulse generator has the luxury of available volume in which to house its power , electronics and control systems . a cranium mounted system , however , is greatly restricted in volume and depth . yet , the ipg 20 has all of the features deemed important to the application within the volume constraints described . the key features of the dbs system 10 shown in fig1 and 2 are summarized below : 1 4 to 16 electrode contacts . 2 4 channels , comprised of any combination within the 16 contacts . 3 individual cathode and anode amplitude control . 4 rechargeable battery . 5 tool - less connector . 6 small package . 1 inductively charged from 2 - 3 cm . 2 80 % charged in 4 hours . 3 at 10 yrs , 1 channel typical discharge in approximately 30 days ; 4 channels typical discharge approximately 7 days . 4 ipg battery status monitoring with telemetry to hand held programmer ( hhp ). 5 battery control and safety circuitry for 100 % failsafe operation . 1 up to 16 electrodes and case ground , individually controlled : biphasic pulse current , frequency , pulse width , channel assignment , monopolar or multipolar operation . 2 up to 4 channels : channel = common frequency and pulse duration for channel assigned electrodes ( electrodes can operate in up to four channels ). 3 amplitude : each electrode : 0 - 12 ma cathodic or anodic current in discrete steps , e . g ., steps of 0 . 1 ma . simultaneous output : ± 20 ma ( distributed ) 4 pulse width : 25 μs ( microseconds ) to 1 ms ( millisecond ), in 10 μs steps ( equal for electrodes on a channel ). 5 rate : 2 ranges including normal , 0 - 150 pps per channel in approximately 1 pps steps , and high rate ( 1 channel ) 160 - 1200 in approximately 10 pps steps . 6 channel timing : channel rates are regulated to prevent overlap with a method that is transparent to the patient . 7 anode control : 3 modes — monopolar case ( any electrode ( s ) (−) to case ), passive anodes ( electrodes connected to ground ), and active anode with individual amplitude control . 8 charge balance : assured through capacitor interface between electrode and output circuitry . 9 soft start : from 1 to 10 seconds , in 1 second steps . 10 run schedule : all channels of the implant turn on and off to the last stimulation settings at preset programmed times . 11 impedance : monopolar at 4 ma : 500 ohms typical . a . battery capacity : automatic telemetry data retrieval initiated by external programmer communication . b . electrode impedance : automatic telemetry data retrieval initiated by external programmer communication . c . confirmations : programmable parameter changes from external equipment confirmed with back telemetry . d . programmed settings : automatic telemetry data retrieval of all programmable settings initiated by external programmer communication . a . two connector sections with up to 16 total electrical contacts for a removable lead system with strong , reliable electrical performance ( low current spread ) under implanted conditions . b . although the connection is typically made only once for any device , the connector mechanism is designed to withstand a minimum of 10 insertions . c . the lead connector system utilizes a simple method to secure the electrode leadwire with a single setcrew per lead . a . intuitive user interface . b . back - lighted flat panel screen . c . hidden physician screen . d . 2 - 3 foot rf range . e . implant battery monitor . f . run time scheduler . g . 4 program storage . h . infrared communication link to clinician &# 39 ; s programming system . a block diagram showing the hybrid configuration of the ipg 20 in accordance with a preferred embodiment of the invention is shown in fig3 . as seen in fig3 , the microprocessor 21 lies at the heart of the ipg . rf telemetry tx / rx circuits 29 interface with the processor 21 . included in the telemetry circuits 29 are an antenna , impedance matching tuning amplifier , and the like . sram memory 23 , when used , and seerom memory 24 provide storage for data and control signals associated with the operation of the processor 21 . the processor 21 controls digital ic 26 and directs it to generate appropriate stimulation currents for delivery through the leads 30 and 30 ′ and electrodes 32 and 32 ′. the digital ic 26 , in turn , controls analog ic 25 so as to generate the stimulus currents . connection with the lead ( s ) 30 , 30 ′ is made through a capacitor array , so that all electrodes are capacitor coupled . a header connector 22 facilitates detachable connection of the lead ( s ) 30 , 30 ′ with the ipg 20 . a rechargeable battery 27 , e . g ., a lithium - ion battery , powers operation of the ipg 20 . a charger coil 19 provides a means for coupling energy into the battery for recharging . battery charger and protection circuits 28 receive the power for recharging the battery through the charger coil 19 ; regulate and distribute power to the rest of the ipg 20 , as required , and monitor the status of the rechargeable battery 27 . in operation , because the system functions as an open - loop system , there is no need for feedback signals , or other signals , derived from physiological event sensors , or the like , that are needed to condition or control the operation of the stimulation pulses that are generated . rather , all that is required is that the individual parameters associated with a given electrode , or group of electrodes , be programmed to desired values . such values may include , e . g ., pulse amplitude , pulse width , pulse shape , and pulse frequency . other stimulation variables may also be programmed , as needed or required for a particular application , e . g ., dose rate , dose duration , ramp rate ( as where the amplitude of the applied stimuli is ramped up from a low or zero amplitude to a desired amplitude ), and the like . significantly , from the patient &# 39 ; s point of view , perhaps one of the more important parameters that the patient , or a patient care - giver , can adjust is simply to turn the system on or off . as described above , it is seen that the invention provides a dbs system that advantageously incorporates a replenishable power source , e . g ., a rechargeable battery , as part of , or coupled to , an implanted pulse generator . the power source may then be replenished , as required , in order to afford a long operating life for the dbs system . as further described above , it is seen that the invention , in accordance with one embodiment thereof , provides a dbs system that capable of delivering stimulation pulses to the brain through selected electrodes on up to two electrode arrays . such arrays are connected to a single , multichannel pulse generator . use of two arrays allows bilateral stimulation of the brain to be provided , if needed . as still further described above , it is seen that the invention provides a dbs system which is programmable , thereby allowing individual stimulation parameter values to be customized for a particular patient . additionally , the dbs system operates in an open loop manner , thereby allowing the circuitry used within the system to remain simple and compact , yet provide needed , and adjustable stimulation therapy , for treatment of targeted disorders . while the invention herein disclosed has been described by means of specific embodiments and applications thereof , numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims .
a deep brain stimulation system provides a multiplicity of stimulation channels through which electrical stimuli may be delivered deep within the brain of a patient . the dbs system is powered by a rechargeable battery . in one embodiment , the system has four channels driving sixteen electrodes . the dbs system is easily programmed for use by a clinician using a clinician programming system , and further affords a simple but highly advanced hand held programmer control interface through which the patient may easily change stimulation parameters within acceptable limits . the dbs system includes a small , implantable pulse generator that is small enough to be implanted directly in the cranium of the patient , thereby eliminating the long lead wires and tunneling procedures that have been used in the past . the implantable pulse generator provides electrical stimuli in an open - loop fashion as defined by the stimulation parameters . further , the dbs system allows up to two electrode arrays to be attached to the implantable pulse generator , thereby eliminating the requirement for implanting two independent implantable pulse generators for bilateral stimulation of deep brain structures .