User Manual
Contents
1. Model PDQ150b PDQ200b Inputs Differential to eliminate ground loops and noise Zin 22 KQ Voltage 30 to 150V 30 to 200V Current 2A Peak D 1 5A Peak 7 Dynamic Current Limiting Dynamic Current Limiting Charge Gain 2 2 6 2 22 62 220 uC V or Custom Voltage Gain 20 66 V V Offset From OV to Full Range with front panel adjustment Connectors BNC input BNC Monitor Outputs LEMO 0B HV Output Bandwidth Greater than 80 kHz 1uF Load Power Bandwidth 9 5 kHz 7 2 kHz Overload Thermal current and voltage overload protection Noise Low noise lt 3 mV RMS Environment 0 40 C 82 104 F Non condensing humidity Enclosure Rugged desktop enclosure 19 inch rack compatible Minimum voltage range V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 3 Output Connection Diagram The output connector is a 2 way LEMO OB socket LEMO EGG 0B 302 CLL The mating plug is a LEMO 0B 2 Way Straight Cable Plug Ordering details and specifications are listed below These parts can be obtained directly from www mouser com Plug Crimp Terminal Version Solder Tag Version Max Conductor Size Cable Collet Cable Diameter Strain Relief Boot LEMO 0B 2 Way Straight Cable Plug LEMO FGG 0B 302 CYCZ LEMO FGG 0B 302 CLAZ AWG22 FGG 0B 742 DN 3 1mm 4mm GMA 0B 035 DN 3 5 3 9mm Cable Supplied with amplifier Note that the crimp terminal plug requires a tool if th2. 10 10 10 Frequency Hz Frequency response for a range of load capacitances The small signal frequency response for a range of capacitive loads is plotted in the above Figure The load capacitances are the maximum permitted under each charge range which results in a voltage gain of 20 When the load capacitance is lower and the voltage gain is increased the bandwidth may be reduced The 3dB bandwidths are listed below Load Capacitance Bandwidth 0 1 uF 200 kHz 1 0 uF 84 kHz 10 uF 27 kHz 100 uF 2 7 kHz Approximate bandwidth versus load capacitance V4 August 2011 PiezoDrive PDQ High Speed Charge Drives Actuator Capacitance versus Bias Voltage and Temperature The power bandwidth slew rate and small signal bandwidth of a piezoelectric amplifier are all primarily limited by the actuator capacitance Larger actuators and actuators with a greater number of internal layers have a higher capacitance Care must be taken when interpreting the capacitance values specified by actuator manufacturers These values are measured at room temperature and with zero bias voltage Due to the non linearity of piezoelectric dielectrics the small signal capacitance increases with higher electric field A capacitance increase of up to 300 has been reported over the full voltage range of a common piezoelectric actuator Hence when predicting the performance of piezoelectric amplifiers a conservative estimate of
3. PiezoDrive PDQ High Speed Charge Drives Peak Current Limit During normal operating conditions with a capacitive load the amplifier is protected a peak current limit If the maximum output current is exceeded the amplifier will behave like a constant current source and the Overload indicator on the front panel will light As an example consider a capacitive load driven by a square wave The output voltage and current wave forms are shown below At each transition the amplifier enters current limit Voltage Current thax hmax Average Current Limit In addition to the peak current limit there is also an average current limit that protects the amplifier from short circuit If the average current limit engages the amplifier will enter an overload condition and the output circuit will be disabled for approximately 5 seconds The positive average current is computed by measuring the current flowing out of the amplifier The current measurement is rectified then averaged with a leaky integrator An identical circuit exists for the negative average current The time constant of the leaky integrator is 270ms which is equivalent to a maximum pulse length of approximately 100ms A benefit of the average current limit is that current pulses less than the peak current are allowed for longer periods of time The maximum non repetitive pulse duration versus the output current is shown below V4 August 2011 PiezoDrive PDQ High Spee
4. The table below lists some experimentally measured output noise voltages These values were recorded with a load capacitance equal to the maximum permitted in that charge range Smaller load capacitances may result in higher noise voltages due to the greater voltage gain Ponies Bandwidih Noe EME 0 1 uF 200 kHz 3 mV 1 0 uF 84 kHz 1 5 mV 10 uF 27 kHz 1 mV Measured noise versus load capacitance The noise was measured with a FLUKE189 TrueRMS Multimeter The bias voltage was 30V and the input was short circuited V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 9 Overload Protection There are two overload indicators on the front panel Overheat and Overload The Overload indicator will illuminate if there is more than 2 Volts difference between the desired output voltage and the actual output voltage This can occur if the maximum current limit is exceeded or if the bandwidth of the input signal is too high This overload indicator does not represent a fault condition and is present mainly to alert the user that the input signal is not being faithfully reproduced The Overheat indicator will illuminate during a shutdown caused by an average current overload or if the amplifier overheats as a result of excessive ambient temperature poor air flow or fan failure None of these conditions should occur during normal operation Hence if an overheat shutdown occurs the amplifier and attached actuator
5. available the amplifier will enter a thermal overload state as discussed in the previous section The PDQ amplifiers can be bolted together in a side by side two channel arrangement With the addition of rack mount handles this configuration can be mounted into a standard 19 inch rack A 19 inch rack mount kit is also available for a single amplifier V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 11 Power Supply Line Voltage 3AG Fuse 6 35 x 32 mm 115 Vac 50 60 Hz 5A 250V Time Delay 230 Vac 50 60 Hz 2 5A 250V Time Delay Mains power is supplied through an IEC connector on the back panel The IEC socket also contains the fuses and operating voltage selector switch Two fuses are required one for each of the active and neutral lines The fuses are located in the back panel power connector and can be accessed by removing the power connecter and lifting out the fuse holder with a screw driver When changing the fuses be certain that the supply voltage selector remains at the correct voltage Maximum power consumption is 200W The PDQ amplifiers require an earthed supply for safe operation 12 Options 19 inch rack mounting kit for two amplifiers 19 inch rack mounting kit for a single amplifier 13 Warranty Support PiezoDrive amplifiers are guaranteed against manufacturing defects for a period of 3 months Technical support contacts can be found at www piezodrive com V
6. current ranges as shown in the above table These models are designed for general purpose and scanning applications where peak current may last for up to 100ms This section contains an introduction to driving capacitive loads followed by a description of the Peak Current Limit and Average Current Limit Driving Capacitive Loads With a capacitive load the required output current is proportional to the rate of change in voltage that is Jac dt where is the current C is the load capacitance and dV dt is the rate of change in voltage Thus more current is required for fast edges or transitions larger amplitudes and higher frequencies The voltage and current waveforms for a sinusoidal voltage and capacitive load are shown below Voltage w Of N Current thnax hax V4 August 201 1 PiezoDrive PDQ High Speed Charge Drives The maximum required current is Imax VpptCf where Imax is the maximum positive and negative current V is the peak to peak amplitude i e double the amplitude fis the frequency and C is the load capacitance For a triangular signal the voltage and current waveforms with a capacitive load are shown below Voltage w KA ge Current lmax hmax The maximum required current is Imax Vpp2Cf where Imax is the maximum positive and negative current V is the peak to peak amplitude i e double the amplitude fis the frequency and C is the load capacitance V4 August 2011
7. peak current The peak current should not exceed 2 x lay which implies 2 X lay Vpp2Cf Thus the maximum frequency of a triangular wave is similar to that of a sine wave lav Yop fmax V4 August 2011 PiezoDrive PDQ High Speed Charge Drives The approximate power bandwidth for a range of capacitive loads is shown below Load PDQ150 PDQ200 Capacitance Power Bandwidth Power Bandwidth 150Vp p Sine wave 200Vp p Sine wave 100 nF 9 5 kHz 7 2 KHz 300 nF 9 2 kHz 7 2 kHz 1 0 UF 4 2 kHz 23 kHz 3 0 pF 1 4 kHz 790 Hz 10 WF 424 Hz 230 Hz 30 pF 141 Hz 79 Hz 100 uF 42 Hz 23 Hz Approximate Power Bandwidth Versus Capacitive Load With very small loads the power bandwidth is limited by the slew rate which is approximately 4 5 V uS The maximum frequency imposed by the slew rate is 4 5 x 10 fj TV yp The maximum peak to peak amplitude and frequency of a sine wave versus frequency is plotted below Maximum Peak to Peak Voltage in V Se a 100uF 30uF 10uF 3uF 1uF 300nF PDQ200b 200 L 150 50 0 E b b hE bo b hE bo b bhbhhbbE bo 4 10 10 10 10 Frequency Hz Maximum sine wave amplitude versus frequency V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 8 Noise Performance The PDQ drives provide extremely low noise and are designed to exceed the requirements of positioning and imaging systems with sub atomic resolution
8. zero by turning the knob counter clockwise 4 Use a signal generator to produce a 20 Hz 1 V peak to peak 0 34 Vrms sine wave with an offset voltage of 1 V The signal should resemble the plot below Input Signal Voltage 5 Turn the amplifier on connect the input signal and observe the output voltage using the Voltage Monitor Turn the DC gain knob clockwise until the offset voltage is equal to the peak to peak voltage The output voltage waveform should resemble the input signal plotted above This calibration can be performed with an oscilloscope or multimeter V4 August 201 1 PiezoDrive PDQ High Speed Charge Drives When using a multimeter the DC gain knob should be turned clockwise until the DC voltage is equal to 2V2 x AC voltage When using an oscilloscope ensure that the input coupling is set to DO The above procedure will equate the voltage gain at DC and 20 Hz It is important to note that many piezoelectric actuators exhibit a significant amount of creep Creep is a non linearity phenomenon that effectively increases the actuator sensitivity and capacitance at low frequencies This may result in increased gain at low frequencies when using the calibration procedure discussed above To avoid the effects of creep the procedure discussed above can be modified Rather than equating the voltage gain at DC and 20 Hz the voltage gain can be equated at 1 Hz and 20 Hz In this case Step 5 is replaced by 5
9. 4 August 2011
10. PiezoDrive PDQ High Speed Charge Drives PiezoDrive PDQ Charge Drives Manual and Specifications PiezoDrive Newcastle Innovation Ltd Industry Development Centre University Drive Callaghan NSW 2308 Australia www piezodrive com V4 August 2011 PiezoDrive PDQ High Speed Charge Drives Warnings Notes 1 The only connection to the output should be a capacitive load or piezoelectric actuator The output of a charge drive is high impedance and cannot be connected to instruments such as a multimeter or oscilloscope 2 Charge drives work differently than voltage amplifiers Section 1 of this manual should be thoroughly reviewed before attempting to operate a charge drive 3 This device produces hazardous potentials and should only be used by suitably qualified personnel under the supervision of an observer with appropriate first aid training Do not operate the device when there are exposed conductors High Voltage V4 August 2011 PiezoDrive PDQ High Speed Charge Drives PiezoDrive PDQ Series High Speed Charge Drives Manual and Specifications Contents 1 Using a Charge Drive a Introduction b Setting the DC Gain c Basic use d Example application e Considerations when using a charge drive Brief Specifications Output Connection Diagram Inputs and Outputs Bandwidth Output Current Limitations Power Bandwidth Noise Performance Overload Protection Enclosure and Thermal Considerations Powe
11. Turn the amplifier on and observe the output voltage using the Voltage Monitor Record the peak to peak or RMS output voltage Reduce the input signal frequency to 1 Hz Turn the DC gain knob clockwise until the output voltage reaches the previously recorded value The voltage gain at 1 Hz and 20 Hz are now equal Since the input and output voltages are known or measured in the above procedure the voltage gain can also be calculated This gain is useful for calculating the maximum input voltage that can be applied before saturation occurs Alternative Procedure for setting the DC gain An alternative method for calibrating the DC gain is to 1 Follow steps 1 to 3 above 2 Apply a 1 Hz square wave to the input with a minimum value of OV anda maximum value of 1V 3 Observe the load voltage by connecting the voltage monitor to an oscilloscope Ensure that the oscilloscope coupling is set to DC 4 Turn the DC Gain knob clockwise until the measured output voltage is a flat square wave proportional to the input C Basic Use As the voltage gain of a charge drive is not fixed this should first be measured using the technique described in the previous section or predicted from the specifications The voltage gain determines the maximum input signal that can be applied before saturation occurs V4 August 2011 PiezoDrive PDQ High Speed Charge Drives Setting the Offset Voltage Piezoelectric actuators are usually biased at
12. d Charge Drives Maximum Pulse Duration Times 2A Current Limit 2 E p s 1000 Cc 2 tw a 500 V a xs S08 4 0 5 1 1 5 2 1 5A Current Limit 800 F E E jai E j j is oly 5 600 gS Q 400 oO 2 a 200 x 05 T T ie T T a T ak 0 5 0 6 0 7 0 8 0 9 1 1 1 1 2 1 3 1 4 1 5 Peak Current A Fold back current limiting Versus PiezoDrive Dynamic Current Control Some high voltage amplifiers use a current limiting technique referred to as fold back current limiting This technique implies a current limit that changes with the output voltage When the output voltage is high more current can be delivered compared to when the output voltage is zero or negative This is due to the lower power dissipation that occurs when the output voltage is high Since the maximum current is only available at the maximum voltage fold back current limiting is suitable for resistive loads but not capacitive loads like piezoelectric actuators The peak current for a capacitive load can occur at any voltage Fold back current limiting can result in unreliable performance when driving piezoelectric actuators A waveform that may be successfully reproduced with a certain bias voltage may become distorted when the bias voltage is reduced In addition the step response of the amplifier changes depending on the output voltage of the amplifier V4 Aug
13. e resistances cause the output voltage to drift at low frequencies However by setting the ratio of resistances equal to the ratio of capacitances low frequency error can be avoided To maintain a constant voltage gain the required resistance ratio is V4 August 2011 PiezoDrive PDQ High Speed Charge Drives R Cs ETG The parallel resistances effectively turn the charge drive into a voltage amplifier at frequencies below f 1 27R C Although the parallel resistances act to stabilize the voltage gain at low frequencies the amplifier now operates as a voltage source below f and a charge drive above A consequence is that reduction of non linearity only occurs at frequencies above f Practical values of f can range from 0 01 Hz to greater than 10 Hz The cut off frequency f can be reduced by increasing the parallel resistances however a practical limit is imposed by the dielectric leakage of the transducer In addition excessively high resistance values also reduce the immunity to drift and result in long settling times after turn on and other transient events The settling time is approximately 5 27f seconds An ideal compromise between excessively long settling times and good low frequency performance is f 0 1 Hz implying a settling time of 8 seconds after turn on This value of f is adopted in the PDQ charge drives which have a cut off frequency of between 0 03 Hz and 0 1 Hz depending on the load capacita
14. half their maximum voltage To set the offset voltage connect the Voltage Monitor output to a multimeter using a BNC to 4mm Plug cable or suitable adaptor Leave the input grounded or unconnected then turn the device on Keeping in mind that the Voltage Monitor output has a gain of 1 20 V V rotate the offset adjustment until the desired offset voltage is reached D Example Application In this example we compare the response of a Noliac SCMAP07 piezoelectric stack actuator 10 mm long when driven with a voltage amplifier and charge drive The full displacement range of this actuator is 10 5 um at 200 V As the actuator capacitance is 330 nF the 22 uC V charge range was selected This corresponds to a voltage gain of 66 and a cut off frequency of 0 1 Hz The voltage and charge driven displacement response to a 100 Hz 150 V sine wave is plotted below Voltage Driven 14 3 Error Charge Driven 0 65 Error Displacement um 0 0 2 0 4 0 6 0 8 1 Normalized Input Voltage The voltage and charge driven response of a Noliac SCMAP07 actuator The applied signal was a 100 Hz 150 V sine wave Using a voltage amplifier the maximum difference in position between two points with the same applied voltage is 1 1 um or 14 3 of the range Alternatively when the voltage amplifier is replaced by a charge drive the non linearity is reduced to 0 05 um or 0 65 of the range In many applications this magnitude of non linearity can a
15. is is not available the solder tag plug should be used A shielded two conductor cable is required to connect the amplifier to a piezoelectric actuator A recommended cable is the Belden 8451 cable The specifications are listed below Cable Conductor Size Resistance Capacitance Outside Diameter Belden 8451 AWG22 0 64mm diameter 53 mOhms m 115 pF m core core 220 pF m core shield 3 5mm The actuator wiring diagram is shown below Return Female Panel Socket Male Cable Plug Actuator If the cable has a shield it should be connected to the body of the plug via the collet as described on the following page Do not connect the shield to the load or use it as a ground return The Return connection is not ground Do not connect the Return conductor to Earth or Ground for example to measure the output voltage with an oscilloscope The only connection to the output should be the piezoelectric actuator V4 August 2011 PiezoDrive PDQ High Speed Charge Drives LEMO Plug Cable Preparation Taken from LEMO B Series Cable Assembly Instructions Solder Crimp Lie tLe les 130 7 30 170 7 40 LEMO Plug Assembly Taken from LEMO B Series Cable Assembly Instructions 1 Strip the cable as above 2 Slide the strain relief collet nut 1 and collet 3 onto the cable 3 If the cable is shielded fold the shield back over the cable 4 Solder the conductors
16. nce PiezoDrive charge drives are designed for both high performance and ease of use Compared to a standard voltage amplifier there is only one additional control the DC gain which sets the voltage gain at low frequencies The PDQ Charge Drives are preconfigured during manufacture to drive a certain range of capacitance values This means that the charge gain resistance ratios and transition frequency f are all optimally preconfigured and do not require user adjustment The standard capacitance ranges and associated charge gain voltage gain and cut off frequencies are tabulated below Load Capacitance Range 30 100 nF 100 300 nF 0 3 1 0 uF 1 0 3 0 uF 3 0 10 uF 10 1000 uF Cut off Freq fe 0 3 0 1 Hz 0 1 0 03 Hz 0 1 0 03 Hz 0 1 0 03 Hz 0 1 0 03 Hz 0 1 Hz Voltage Gain K 66 22 60 20 66 22 60 20 66 22 40 Charge Gain Kg 2 2 uC V 6 2 uC V 22 uC V 62 uC V 220 uC V Custom Load capacitance ranges of the PDQ drives From the above table it can be observed that the equivalent voltage gain and cut off frequency are both inversely proportional to load capacitance Thus at the smaller end of the load capacitance range the voltage gain and cut off frequency are both near the maximum of 66 and 0 1 Hz respectively Only connect load capacitances of within the specified range For ease of use
17. onto the contacts 5 Assemble the plug V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 4 Inputs and Outputs Voltage Monitor CL Offset Piezoelectric Load Charge Monitor Current Monitor Simplified schematic of the charge drive inputs and outputs Input Circuit The input circuit has a function similar to a unity gain differential amplifier This circuit is designed to eliminate ground loops and noise resulting from the connection of instruments with different power supplies The full scale range of the input circuit is 10V The signal ground is allowed to float by approximately 0 6V before it is electrically connected to ground The input impedance is 22kOhm Offset Voltage After the input stage an optional offset voltage is added to produce an electrical bias of between OV and 200V A typical stack actuator should be biased at half of the full scale voltage Monitor Outputs There are three monitor outputs on the front panel The voltage monitor has a gain of 1 20 V V the charge monitor has a gain equal to the sensitivity of the drive and the current monitor has a gain of 1 V A The maximum output current from the monitor outputs is 10 mA V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 5 Small Signal Bandwidth B i ol 20 Magnitude d 15 l b bh be PERE 3 E k bP PE EE 10 10 10 10 Phase deg 10
18. r Supply Options Warranty Support Confidential Information This document contains confidential information It cannot be distributed without consent This document is subject to change at any time V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 1 Using a Charge Drive A Introduction It has been known since the 1980 s that piezoelectric transducers respond more linearly to current or charge rather than voltage 1 However problems with drift and the floating nature of the load have only been solved recently 2 3 Since then charge drives have been demonstrated to reduce the hysteresis of piezoelectric actuators by up to 93 4 This corresponds to a maximum non linearity of less than 1 that can reduce or eliminate the need for feedback or feedforward control in dynamic applications The simplified schematic diagram of a charge drive is shown below Simplified schematic diagram of a charge drive The piezoelectric load modelled as a capacitor C and voltage source vp is shaded in gray The high gain feedback loop works to equate the applied reference voltage Vin to the voltage across a sensing capacitor C Neglecting the resistances R and R the output charge q is q Vinls That is the gain is Cs Coulombs V This implies an input to output voltage gain of Cs C VIN A major problem with charge drives is the finite output impedance and dielectric leakage modelled by R and R Thes
19. should be thoroughly inspected The most common cause of an overheat shutdown is intermittent short circuits produced by a damaged actuator The behaviour of the amplifier during an average current overload is discussed in Output Current Limitations If the amplifier overheats the output stage is immediately disabled When the temperature returns to a safe level the amplifier will automatically reset This may take a few minutes During an Overheat shutdown caused by excessive average current or temperature the output current reduces to a few mA It is important to note that this does not mean that the output voltage will be zero Dangerous potentials may still exist External Shutdown In addition to the internal shutdown triggers the output stage of the amplifier can also be disabled by applying a positive voltage to the external shutdown connector 2V to 12V The impedance of the external shutdown input is approximately 2 5kQ The external shutdown is useful for implementing thermal protection of an actuator or for disabling a feedback system V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 10 Enclosure The PDQ amplifiers are housed in a rugged aluminium desktop enclosure The dimensions are shown below 132 6 mm 5 22 in ee a ee eae 12 0 in 212 6 mm 8 37 in The PDQ amplifiers have a rear air intake and side exhaust vents for cooling These should not be obstructed If sufficient air flow is not
20. the PDQ drives are configured during manufacture for a specific range of load V4 August 201 1 PiezoDrive PDQ High Speed Charge Drives capacitances which are printed on the rear panel A smaller load capacitance is permissible but not recommended since the voltage gain and cut off frequency will be excessively high A load capacitance larger than the specified maximum should never be connected to the output This may result in instability will reduce the output voltage range and can trigger an internal shutdown Always ensure the load capacitance is within the specified range before turning the drive on B Setting the DC Gain Since the charge gain of a PDQ drive is fixed the input to output voltage gain depends on the load capacitance At frequencies above f the voltage gain K is K K v C where K4 is the charge gain and C is the load capacitance If the load capacitance is within the specified range the voltage gain K will be between 20 and 66 At frequencies below f the voltage gain is determined by the DC gain knob on the front panel In most applications it is desirable to have a constant gain over all frequencies so the DC gain should be equated to the AC gain at frequencies above f This can be achieved by following the procedure below Procedure for setting the DC gain 1 Connect the actuator or load capacitance 2 Set the offset voltage to zero by turning the knob counter clockwise 3 Set the DC gain to
21. the actual operating capacitance should be used In typical applications where the bias voltage is half the full range voltage the capacitance value specified by the manufacturer should be multiplied by a factor of 2 In addition to capacitance non linearity piezoelectric dielectrics are also highly temperature dependant For example the sensitivity and capacitance of common piezoelectric actuators can double with every 50 degrees Celsius increase in temperature If the ambient temperature is above 25 degrees Celsius the Capacitance increase must be taken into account Due to dielectric heating large temperature increases can also occur when driving piezoelectric actuators at high speed or full range This is particularly true of small actuators with a low thermal mass a 50 degree temperature increase can occur in just a few seconds of heavy excitation V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 6 Output Current Limitations Model PDQ150 PDQ200 Peak Current I 2A 1 5A RMS Current Lms 1 6A 1 1A Average DC Current I 0 7 A 0 5 A Overload Time 100ms 100ms The PDQ amplifiers contain a new technology called Dynamic Current Control Compared to other amplifiers with fixed current limits Dynamic Current Control allows a larger peak current and the reproduction of larger amplitude waveforms with higher frequency The PDQ amplifiers are available in two voltage and
22. uld be the actuator Since charge drives work like a voltage amplifier at frequencies below f there is no control over extremely low frequency non linearity such as creep References 1 C V Newcomb and I Flinn Improving the linearity of piezoelectric ceramic actuators EE Electronics Letters vol 18 no 11 pp 442 443 May 1982 2 K A Yi and R J Veillette A charge controller for linear operation of a piezoelectric stack actuator IEEE Transactions on Control Systems Technology vol 13 no 4 pp 517 526 July 2005 3 A J Fleming and S O R Moheimani Sensorless vibration suppression and scan compensation for piezoelectric tube nanopositioners EEE Transactions on Control Systems Technology vol 14 no 1 pp 33 44 January 2006 4 A J Fleming and K K Leang Charge drives for scanning probe microscope positioning stages Ultramicroscopy vol 108 no 12 pp 1551 1557 November 2008 5 A J Fleming Quantitative SPM topographies by charge linearization of the vertical actuator Review of Scientific Instruments vol 81 no 10 pp 103701 1 5 October 2010 V4 August 2011 PiezoDrive PDQ High Speed Charge Drives 2 Brief Specifications The PDQ drives are designed to optimize the performance of multilayer piezoelectric stack actuators Brief specifications are listed below Detailed specifications are contained in the following sections
23. ust 2011 PiezoDrive PDQ High Speed Charge Drives 7 Power Bandwidth The PDQ amplifiers are designed to maximize the power bandwidth in general purpose and scanning applications The power bandwidth is the maximum frequency sine wave that can be reproduced at full voltage For capacitive loads the power bandwidth is primarily limited by the load capacitance and current limit An expression for the maximum current of a capacitive load driven by a sine wave was derived in the previous section Imax VpptCf Where V is the peak to peak output voltage C is the load capacitance and fis the frequency Given a peak current limit of Ipx the maximum frequency sine wave is Ink VppTC fmax Since the PDQ amplifiers limit both the peak and average current it is also important to consider the average current requirements The average positive or negative current for a sine wave with a peak current of Lmax iS 1 r7 lav Imax sin d 2T Jo Imax TT Imax lav 27 cos Hence the maximum possible sine wave with a peak current of Imax Ipx requires an average current of I m which is guaranteed by the specifications of the PDQ amplifiers The situation is different for triangular waveforms A triangular waveform requires a peak current of Imax Vpp2Cf and an average current of 1 77 Imax lave Imax d0 7 0 Hence a triangular waveform is limited by average current not
24. void the necessity for feedback or feedforward hysteresis compensation Other examples of charge linearization can be found in the reference list V4 August 2011 PiezoDrive PDQ High Speed Charge Drives This example was reproduced with permission from 5 E Considerations when using a charge drive In many respects a charge drive is similar to a voltage amplifier however there are some important differences that should be considered The PDQ charge drives use a floating load configuration as illustrated by the circuit diagram in Section 1 A In this configuration the return signal path is not ground rather it may float by up to 10 V This means that the actuator load voltage is not exactly the output voltage but the difference between the output voltage and the return path As the charge monitor output is the voltage across the sensing capacitor the exact differential load voltage can be measured using the following equation 1 Differential Load Voltage Voltage Monitor 20 Charge Monitor It is also important to keep in mind that the return signal path is high impedance This means that any resistive or capacitive loads connected to the return path will cause an error This includes multimeters oscilloscopes other instrumentation and especially any ground connectors The return path is also susceptible to electromagnetic interference so it should be kept well shielded The only connection to the output of a charge drive sho
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