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Agilent Technologies 54701A, User'S And Service Manual

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23

Chapter 2: Probing Considerations

Resistive Loading Effects

Resistive Loading Effects

The two major effects caused by resistive loading are amplitude distortion and 
changes in dc bias conditions in the circuit under test. 

Amplitude Distortion    

Amplitude distortion is depicted in figure 7, where waveform 1 is the signal 
before probing and waveform 2 is the signal while probing.  (The baselines of 
these signals have been overlayed to show the amplitude change.  If the 
baseline of a signal is not at zero volts it will shift when the signal is probed.)

Figure 7

Oscilloscope Display Showing Amplitude Distortion

The cause of the error is the voltage divider developed between the source 
resistance of the device under test and the input resistance of the probe being 
used.  Equation 2 calculates the error caused by the voltage divider. 

Equation 2

Error(%) = 

A probe with an input resistance ten times that of the source resistance of the 
device under test causes a 9.09% error in the measurement.  It is best to use a 
probe with an input resistance at least ten times that of the source resistance.

R

source

R

source

R

probe

+

---------------------------------------- 100

×

Waveform 1

Waveform 2

Summary of Contents for 54701A

Page 1: ...Publication number 54701 97003 September 2002 For Safety and Regulatory information see the pages behind the index Copyright Agilent Technologies 1992 2002 All Rights Reserved Agilent Technologies 54701A 2 5 GHz Active Probe ...

Page 2: ...nput resistance of 100 kΩ Input capacitance of approximately 0 6 pF Dynamic range of 5 V peak ac and 50 Vdc Variable dc offset of 50 V Excellent immunity to ESD and over voltages Accessories Supplied The following accessories are supplied See Using probe accessories in chapter 1 for a complete list Type N f to BNC m adapter Walking stick ground Box of small accessories Carrying case User and Servi...

Page 3: ...0B1 Additional User and Service Guide Service Strategy Except for the probe tip there are no field replacable parts in the Active Probe Depending on the warranty status of your probe if it fails it will be replaced or exchanged See chapter 3 Service for further information and how to return your probe to Agilent Technologies for service Option 001 ...

Page 4: ...power connector on the oscilloscope or the separately available 1143A Probe Offset Control and Power Module Chapter 2 gives you information about some important aspects of probing and how to get the best results with your probe Chapter 3 provides service information Included is how to test the probes performance how and when to make the one adjustment and how to determine if your probe needs repai...

Page 5: ... the probe to the 54120 family oscilloscopes 13 Using the probe with oscilloscope power 14 Using the probe with the 1143A power module 15 Using probe accessories 16 Additional Accessories 20 2 Probing Considerations Capacitive Loading Effects 25 Ground Inductance Effects 27 Probe Bandwidth 31 Conclusion 32 ...

Page 6: ...t Equipment 38 Service Strategy 39 To clean the instrument 40 To return the probe to for service 40 To test input resistance 42 To test dc gain accuracy 43 To test bandwidth 45 To adjust offset zero 49 Failure Symptoms 51 To prepare the probe for exchange 53 Replaceable Parts 54 Theory of Operation 56 ...

Page 7: ...7 1 Operating the Probe ...

Page 8: ...be Adapter not supplied order separately 5081 7722A Type N m to APC 3 5 f Adapter supplied as Option 001 or order separately Walking stick Ground supplied N f to BNC m Adapter supplied Included with the probe is a box of small accessories See Page 16 for a complete list of accessories ...

Page 9: ...cally and electrically Check the accessories Accessories supplied with the instrument are listed in Accessories Supplied in table 1 page 16 in this manual If the contents are incomplete or damaged notify your Agilent Technologies sales office Inspect the instrument If there is mechanical damage or defect or if the instrument does not operate properly or pass calibration tests notify your Agilent T...

Page 10: ...quency This is the maximum input voltage that can be applied without risking damage to the probe Figure 2 Maximum Input Voltage vs Frequency Figure 3 shows the operating range of the probe For the most accurate measurements and safety for the probe signals should be within the indicated operating region Figure 3 Probe Operating Range Area of Optimum Operating ...

Page 11: ... curve the level of harmonic distortion in the output is equal to or below that represented by the curve The dashed straight line in each figure represents the operating range limit as shown in figure 3 on the previous page Figure 4 Second Harmonic Distortion Input Voltage vs Frequency Figure 5 Third Harmonic Distortion Input Voltage vs Frequency Second Harmonic 20 dBc Second Harmonic 30 dBc Secon...

Page 12: ...h the connector keys Align the keys when inserting the cable connector into the power connector CAUTION The probe power cable connector automatically locks in the mating power connector To separate the connectors you must pull on the knurled part of the cable connector housing This releases the lock If you pull on the cable the connectors won t release and you may damage the connector or cable If ...

Page 13: ...143A power module for probe power set the Offset controls to Local and Zero while performing the calibration Follow the calibration procedures for your oscilloscope CAUTION An effort has been made to design this probe to take more than the average amount of physical and electrical stress However with an active probe the technologies necessary to achieve high performance do not allow the probe to b...

Page 14: ...s the offset range is 50 V See the sidebar below Since the 54701A is an active probe the bandwidth of the oscilloscope and probe combination is a mathematical combination of their individual specifications Equation 1 System Bandwidth where tr1 is the risetime of the oscilloscope tr2 is the risetime of the probe If you are using a 54700 family oscilloscope the resultant bandwidth with a specific ma...

Page 15: ...oscope has an offset feature be sure that it is set to zero so that the probe offset does not have to compensate for the oscilloscope offset 7 If necessary adjust the Coarse and Fine offset controls so the desired part of the signal is displayed on the oscilloscope See sidebar below The offset range is greater than 50 V relative to the probe tip Bandwidth issues are the same as covered on the prev...

Page 16: ... 1250 0077 2 Walking stick ground 1 5960 2491 3 Single contact socket 5 1251 5185 4 Standard probe pin 5 54701 26101 5 Sharp probe pin 2 5081 7734 Nut Driver 3 32 in not shown 1 8710 1806 6 200 Ω signal lead 1 54701 81301 7 Ground extention lead 1 0650 82103 8 Alligator ground lead 1 01123 61302 Flexible Probe Adapter 1 54701 63201 Probe Socket 1 5041 9466 Coaxial Socket 3 1250 2428 Operating and ...

Page 17: ...k ground the 200 Ω signal lead and the ground extention lead Probe Pins There are two types of replaceable probe pins furnished with the probe The 0 030 inch round standard probe pin is for general applications It is made of a material that will generally bend before breaking The 0 025 inch round sharp probe pin has a narrower point and is a harder material It can be used to probe constricted area...

Page 18: ... stick to the circuit under test When used with the walking stick ground the probe resonance is damped by the bead on the walking stick Alligator Ground Lead The alligator ground lead can be used in general applications when the bandwidth of the signal is 350 MHz or lower With no signal lead extention the probe resonant frequency is about 650 MHz Flexible Probe Adapter The flexible probe adapter p...

Page 19: ...The coaxial socket is designed to fit the standard mini probe When used with the flexible probe adapter it can be installed in a circuit so you can probe with the 54701A The illustration shows the socket and the PC board layout needed to mount the socket to the board See Also Chapter 2 Probing Considerations for a more complete discussion about the effects of probe connection techniques on signal ...

Page 20: ...ther adapters can compromise signal fidelity and may be vulnerable to mechanical damage This adapter can be ordered with the probe as Option 001 Type N to Probe Tip Adapter The 11880A Type N m to probe tip adapter is available to connect the input of the active probe to Type N connectors It has an internal 50 Ω load It can be used for general testing and is specifically recommended for testing the...

Page 21: ...21 2 Probing Considerations ...

Page 22: ... how the probe affects the circuit during the measurement When a probe is connected to a circuit to measure a signal it becomes part of the circuit Probing a signal can be easy and successful if some forethought is given to the nature of the circuit under test and what type of probe best solves the measurement problem Because of the wide variety of signals that may be encountered ranging from high...

Page 23: ... baseline of a signal is not at zero volts it will shift when the signal is probed Figure 7 Oscilloscope Display Showing Amplitude Distortion The cause of the error is the voltage divider developed between the source resistance of the device under test and the input resistance of the probe being used Equation 2 calculates the error caused by the voltage divider Equation 2 Error A probe with an inp...

Page 24: ...cting the probe sources current into the output node which reduces the current sourced from the gate output The output current drops from 4 2 mA to 0 7 mA The low output current can cause problems with switching noise margins The output gate will have difficulty reaching the low threshold so ac performance will suffer because the falling edge degrades If a larger bias resistor had been used to kee...

Page 25: ...probes a 1 MΩ 6 pF probe and the 54701A probe 100 kΩ 0 6 pF It shows that because of the lower input capacitance the 54701A probe actually has a higher input impedance for frequencies above 240 kHz At frequencies above 2 65 MHz it has as much as 10 times the impedance of the 1 MΩ probe Figure 9 Probe Impedance vs Frequency The input capacitance of a probe forms an RC time constant with the paralle...

Page 26: ...5 pF probe Figure 10 Spice Simulation Of Probe Capacitance Loading Effects Table 2 summarizes the data It shows that the 6 pF probe didn t significantly increase the rise time of the signal but delayed it referenced at the 50 point approximately 150 ps The 15 pF probe not only slowed the rise time approximately 33 but also delayed the edge 340 ps Table 2 Probe Capacitance Loading Effect Plot Riset...

Page 27: ...g use the shortest possible ground with a probe that has the lowest possible input capacitance Equation 3 can be used to calculate the frequency where a certain probe and grounding technique resonates Equation 3 fr where C is the probe input capacitance It is usually found in the probe data sheet L is the inductance of the ground return It can be approximated using the constant of 25 nH per inch F...

Page 28: ...28 Chapter 2 Probing Considerations Resistive Loading Effects Figure 11 Probe Impedance and Resonance 1 MΩ 6 pF probe 1 MΩ 6 pF probe ...

Page 29: ...surement and the calculation yield the same result showing how probe resonance causes problems when probing high speed signals Waveform 2 shows the pulse response when the same 6 pF probe measures an 800 ps edge Notice that the overshoot and ringing are still present but are significantly reduced This is because the slower signal edge has less energy at the resonant frequency of the probe Waveform...

Page 30: ...tion 4 This equation is derived from a first order RC response Equation 4 Bandwidth Example The 1 25 ns edge waveform 3 in figure 12 equates to a 280 MHz bandwidth Bandwidth This is approximately half the resonant frequency calculated for the 6 pF probe with 1 2 inch ground 580 MHz Therefore the subdued ringing on waveform 3 validates the rule of thumb As noted before waveform 4 shows the effect w...

Page 31: ...any errors Equation 5 where tr1 is the rise time of the probe tr2 is the rise time of the signal 1 Calculate the rise time of the 700 MHz probe equation 4 2 Calculate the rise time of the 1 ns signal as measured by the 700 MHz probe equation 5 The measurement error between the actual signal and what was measured is 12 To keep measurement errors less than 6 use a probe with a band width three or mo...

Page 32: ...The 0 6 pF input capacitance of the 54701A probe is about 3 to 6 that of the circuit capacitance It will not significantly change the time constant in the node being probed Ground Inductance The CMOS gate has a risetime approaching 1 ns This equates to a bandwidth of 350 MHz equation 4 If we use the walking stick ground about 20 nH provided with the 54701A probe the probe resonance will be about 1...

Page 33: ...33 3 Service ...

Page 34: ...er provides service information for the 54701A Active Probe The following sections are included in this chapter Specifications and Characteristics Returning for Service Calibration Testing Procedures Making Adjustments Troubleshooting and Repair ...

Page 35: ...he following general information applies to the 54701A 2 5 GHz Active Probe Specifications Table 3 gives specifications used to test the active probe Table 3 Specifications Attenuation Factor 10 1 Bandwidth 3dB 2 5 GH dc Gain Accuracy 0 5 Input Resistance 100 kΩ 1 ...

Page 36: ...olerance 150 Ω 150 pF 12 kV Flatness 3 ns from rising edge 6 3 ns from rising edge for input edge 170 ps 1 Dynamic Range 1 5 gain compression 5 V peak ac and 50 Vdc Offset Adjustment Range referenced to the probe tip 50 V Offset Accuracy 1 of offset 1 mV Offset Gain referenced to the probe tip 11 5 V mA RMS Output Noise dc to 2 5 GHz input loaded by 50 Ω 300 mV Propagation Delay 7 5 ns approximate...

Page 37: ...104 F up to 90 relative humidity at 65 C 149 F Altitude up to 4 600 meters 15 000 ft up to 15 300 meters 50 000 ft Vibration Random vibration 5 to 500 Hz 10 minutes per axis 0 3grms Random vibration 5 to 500 Hz 10 min per axis 2 41 grms Resonant search 5 to 500 Hz swept sine 1octave min sweep rate 0 75g 5 min resonant dwell at 4 resonances per axis Power Requirements 17 Vdc and 17 Vdc at 110 mA ea...

Page 38: ...on listed in the table Product Regulations Safety IEC 348 UL 1244 CSA C22 2 No 231 Series M 89 EMC This product meets the requirement of the European Communities EC EMC Directive 89 336 EEC Emissions EN55011 CISPR 11 ISM Group 1 Class A equipment SABS RAA Act No 24 1990 Immunity EN50082 1 Code1 Notes2 IEC 801 2 ESD 4 kV CD 8kV AD 1 IEC 801 3 Rad 3 V m 1 IEC 801 4 EFT 1kV 1 1 Performance Codes 1PAS...

Page 39: ...for further information Recommended Test Equipment Equipment Required Critical Specifications Recommended Model Part Use Signal Generator 50 MHz to 2 5 GHz 8663A C Power Meters 2 or one Dual Channel 50 MHz to 2 5 GHz 3 accuracy 436A 2 437A 2 or 438A 1 C Power Sensor 2 50 MHz to 2 5 GHz 300 mW 8482A C Power Splitter dc to 2 5 GHz 0 2 dB output tracking Type N 11667A C Power Supply Power and control...

Page 40: ...move all accessories from the instrument Accessories include all cables Do not include accessories unless they are associated with the failure symptoms 3 Protect the instrument by wrapping it in plastic or heavy paper 4 Pack the instrument in foam or other shock absorbing material and place it in a strong shipping container You can use the original shipping materials or order materials from an Agi...

Page 41: ...on requirements The calibration cycle is covered in the Making Adjustments section in this chapter Equipment Required A complete list of equipment required for the calibration tests is in the Recommended Test Equipment table on page 41 Equipment required for individual tests is listed in the test Any equipment satisfying the critical specifications listed may be substituted for the recommended mod...

Page 42: ...probe tip and the ground shell at the front of the probe 2 Set up the DMM to measure resistance The resistance should read 100 kΩ 1KΩ 3 Record the reading in the Calibration Test Record on page 47 Equipment Required Equipment Critical Specification Recommended Model Part Digital Multimeter Resistance 0 1 3458A If the test fails Go to the Troubleshooting and Repair section in this chapter ...

Page 43: ... module set the Offset controls to Local and Zero If using an oscilloscope for probe power use the channel menu to set the offset to 0 0 V 5 Short the input pin of the probe to the shield at the probe tip You can use the 11880A see To test bandwidth on page 45 which is an Type N to probe tip adapter with an internal 50 Ω termination The objective is to effectively short the probe input without ind...

Page 44: ...ep 6 from the reading in step 8 _____________mV The result should be 500 mV 2 5 mV 10 Calculate the dc gain The dc gain should be between 0 09950 and 0 10050 0 10 0 5 11 Record the results of step 10 in the Calibration Test Record on page 50 result in step 9 5 00 V supply voltage If the test fails Go to the troubleshooting section in this chapter If the offset voltage is greater than 1 0 mV If the...

Page 45: ...ule set Offset controls to Local and Zero If using an oscilloscope for probe power use the channel menu to set the offset to 0 0 V 5 Set the signal generator for 50 MHz at 0 0 dBm 6 Set the power meter calibration factors to the 50 MHz value on the power sensors Equipment Required Equipment Critical Specifications Recommended Model Part Signal Generator 50 MHz to 2 5 GHz 8663A Power Meters 2 or on...

Page 46: ...tio of the probe 9 Change the signal generator frequency to 2 5 GHz 10 Set the power meter calibration factors to the 2 5 GHz value on the power sensors 11 Re level the signal generator output power for a 6 0 dBm reading on the input power meter 12 Note the power level reading on the output power meter 2 5 GHz power level _______________ dBm 13 Subtract the reading in step 8 from the reading in st...

Page 47: ...________ Work Order No ____________________ Recommended Test Interval 1 Year 2000 hours Date____________________ Recommended next testing_________________ Temperature_____________ Test Limits Results Input Resistance 100 kΩ 1 99 0 kΩ to 101 0 kΩ _____________ dc Gain Accuracy 0 10 0 5 0 09950 to 0 10050 _____________ Bandwidth down less than 3 dB at 2 5 GHz _____________ ...

Page 48: ...ment that satisfies the critical specification listed in the table may be substituted for the recommended model Equipment for individual procedures is listed at the procedure Adjustment Interval There is no defined adjustment interval for the active probe The adjustment is considered a factory adjustment and does not require periodic maintenance Make adjustments only when directed by other service...

Page 49: ... tip adapter used in the bandwidth test It has an internal 50 Ω termination The objective is to effectively short the probe input without inducing any signal Another method can be used if it provides the same result 5 Terminate the output of the probe with the N to BNC adapter and BNC 50 Ω feedthrough 6 Connect the probe power connector to the 1143A power module or an oscilloscope with the appropr...

Page 50: ...een wire of the cable connector and record the voltage reading _______________mV This voltage is typically less than 5 mV Measure it with 10 mV resolution 12 Multiply the reading in the previous step by 2 3 Observe the signs _______________mV 13 Connect the DVM to measure the voltage between ground and the output of the probe at the 50 Ω feedthrough 14 Adjust R13 for a reading the same as the resu...

Page 51: ...tion Fails Probe calibration failure with an oscilloscope is usually caused by improper setup If the calibration will not pass check the following Be sure the instrument passes calibration without the probe Check that the probe passes a signal with the correct amplitude If the probe is powered by the oscilloscope check that the offset is approximately correct The probe calibration cannot correct m...

Page 52: ...cy of the dc gain requires factory repair Incorrect Input Resistance First check that the probe tip is not loose The input resistance is determined in the amplifier hybrid in the probe and cannot be repaired in the field The probe must be returned to the factory for repair Incorrect Offset Incorrect offset can be caused by a misadjusted offset zero see Offset Will Not Zero on the next page lack of...

Page 53: ... adjust offset zero in chapter 2 of the 1143A User and Service Guide To prepare the probe for exchange If your probe is out of warranty and you want to exchange your failed probe for a reconditioned probe you need to keep the cover plate that holds the probe serial number The reconditioned probe will not have a serial number When you receive the reconditioned probe put your cover plate with serial...

Page 54: ...ts center in California USA No maximum or minimum on any mail order there is a minimum amount for parts ordered through a local Agilent sales office when the orders require billing and invoicing Prepaid transportation there is a small handling charge for each order No invoices In order for Agilent Technologies to provide these advantages please send a check or money order with each order Mail orde...

Page 55: ...55 Chapter 3 Service Troubleshooting and Repair MP4 Foam set 1 5041 9442 MP5 Label carrying case 1 5090 4488 MP6 Plastic parts box 1 1540 0022 Replaceable Parts Ref Des Description Qty Part Number ...

Page 56: ...e Circuitry All of the probe circuitry is constructed on a ceramic substrate with discrete parts and two operational amplifier chips The circuit is a two path amplifier one path for the high frequency component of the signal and one for the low frequency component Input Divider The signal is divided twice in the input impedance network It is divided by ten and fed to the high frequency amplifier A...

Page 57: ...dth product of U1 limits the frequency response of the low frequency amplifier to 400kHz U1 drives the base of the common base stage Power Box Circuitry Power Box CircuitryThe probe signal is fed via the coaxial cable directly through the power box to the Type N connector The power box takes five inputs from the probe power connector and conditions them for the probe The probe power inputs are Two...

Page 58: ...58 Chapter 3 Service Troubleshooting and Repair ...

Page 59: ... loading 25 26 probe resonance 27 30 resistive loading 23 24 exchanging 53 F failure symptoms 51 G gain accuracy testing active probe 43 ground inductance 27 32 H harmonic distortion 11 I input capacitance 27 input resistance oscilloscope 12 input resistance testing active probe 42 inspecting 9 instrument cleaning the 63 L limiting probe offset 14 15 lock probe power cable 12 M maximum input volta...

Page 60: ... strategy 3 39 specifications 35 storage environment 37 T terminating probe 12 test equipment required 39 test interval 41 test record 41 testing active probe bandwidth 45 dc gain accuracy 43 input resistance 42 testing performance 41 theory 56 troubleshooting 51 55 W weight 37 ...

Page 61: ...5 EN 61000 4 5 1995 IEC 61000 4 6 1996 EN 61000 4 6 1996 IEC 61000 4 11 1994 EN 61000 4 11 1994 Canada ICES 001 1998 Australia New Zealand AS NZS 2064 1 Limit Group 1 Class A 1 4 kV CD 8 kV AD 3 V m 80 1000 MHz 0 5 kV signal lines 1 kV power lines 0 5 kV line line 1 kV line ground 3 V 0 15 80 MHz 1 cycle 100 Safety IEC 61010 1 1990 A1 1992 A2 1995 EN 61010 1 1993 A2 1995 Conformity Supplementary I...

Page 62: ...0 4 5 1995 EN 61000 4 5 1995 IEC 61000 4 6 1996 EN 61000 4 6 1996 IEC 61000 4 11 1994 EN 61000 4 11 1994 Canada ICES 001 1998 Australia New Zealand AS NZS 2064 1 A B A A A A 1Performance Criteria A PASS Normal operation no effect B PASS Temporary degradation self recoverable C PASS Temporary degradation operator intervention required D FAIL Not recoverable component damage Notes none Sound Pressur...

Page 63: ...terminal must be connected to the earth termi nal of the power source Whenever it is likely that the ground protection is impaired you must make the instrument inoperative and secure it against any unintended operation Service instructions are for trained service personnel To avoid dangerous electric shock do not perform any service unless qualified to do so Do not attempt internal service or adju...

Page 64: ...d in this document is provided as is and is subject to being changed without notice in future editions Further to the maximum extent permitted by applica ble law Agilent disclaims all warranties either express or implied with regard to this manual and any information contained herein including but not limited to the implied war ranties of merchantability and fitness for a particular purpose Agilen...

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