LECROY AP034-OM-E-03 OPERATION 电路图.pdf

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1、AP034-OM-E Rev DISSUED: January 2000? ? ? Caution The input circuits in the AP034 Active Differential Probe incorporate components that protect the probe from damage resulting from electrostatic discharge (ESD). Keep in mind that this is an active probe, and it should be handled carefully to avoid d

2、amage. When using the AP034 Active Differential Probe, you are advised to take precautions against potential instrument damage due to ESD. CONNECTING THE PROBE TO THE TEST INSTRUMENT When you are using the AP034 Active Differential Probe with a LeCroy Oscilloscope equipped with ProBus, attach the pr

3、obe output connector to the oscilloscope input connector. The oscilloscope will recognize the probe, set the oscilloscope input termination to 50 ? the user interface. To use the AP034 Active Differential Probe with instrumentation not equipped with a ProBus interface, it is necessary to use the ADP

4、PS Power Supply. Attach the ADPPS connector to the probe output connector. The output connector of the ADPPS is a standard male BNC that can be directly connected to another instrument. If necessary, the output of the ADPPS can be interconnected with a 50 ? of skin loss, this cable should be 1 m or

5、less in length. The AP034 Active Differential Probe is designed to drive a 50 ? The gain will be uncalibrated if the output is not correctly terminated. If you are using the probe with an instrument with a high input impedance, place a 50 ? instrument input before attaching the ADPPS. CONNECTING THE

6、 PROBE TO THE TEST CIRCUIT At the probe tip, two inputs and a ground connection are available for connecting the probe to a circuit under test. For accurate measurements, both the + and inputs must always be RadioFans.CN 收音机爱 好者资料库 ?ISSUED: January 2000AP034-OM-E Rev D ? connected to the test circui

7、t. The ground connection is optional. Positive voltages applied to the + input relative to the input will deflect the oscilloscope trace toward the top of the screen. To maintain the high performance capability of the probe in measurement applications, user care in connecting the probe to the test c

8、ircuit. Increasing the parasitic capacitance or inductance in the input paths may introduce a “ring,” or slow the rise time of fast signals. To minimize these effects, use the shortest length possible when connecting the probe to the circuit under test. Input leads that form a large loop area (even

9、shielded coaxial cables) will pick up any radiated magnetic field that passes through the loop, and may induce noise in the probe inputs. Because this signal will appear as a differential mode signal, the probes common mode rejection will not remove it. You can greatly reduce this effect by using sh

10、ort interconnection leads, and twisting them together to minimize the loop area. High common mode rejection requires precise matching of the relative gain or attenuation in the + and input signal paths. Mismatches in additional parasitic capacitance, inductance, delay, and a source impedance differe

11、nce between the + and signal paths will lower the common mode rejection ratio. Therefore, it is desirable to use the same length and type of wire and connectors for both input connections. When possible, try to connect the inputs to points in the circuit with approximately the same source impedance.

12、 If AC coupling is desired, install the AC coupling accessory on the probe tip before connecting it to the test circuit. The low- frequency cutoff (3 dB point) of the AC coupler is approximately 16 Hz. If the voltage in the test circuit exceeds the probes capability, add the external 10 or 20 attenu

13、ator* to the probe tip. If both the external attenuator and AC coupler are used, install the attenuator on the probe tip first, then install the AC coupler on the attenuator input. * Note The external attenuators are precisely adjusted during manufacturing to match the RadioFans.CN 收音机爱 好者资料库 AP034-

14、OM-E Rev DISSUED: January 2000? ? characteristics of the input of the probe with which they were shipped. The input characteristics of the external attenuator itself do not exactly match those of the probe. Therefore, using the 10 and 20 attenuators at the same time is not recommended. The scale fac

15、tor encoding system will not operate correctly with both attenuators installed simultaneously. The input characteristics of the AP034 1 GHz Active Differential Probe are significantly different than those of the AP033 500 MHz Active Differential Probe. The external attenuators are not interchangeabl

16、e. The external attenuators currently supplied with the probes are labeled with the appropriate model number. The attenuators supplied with model AP033 probes prior to the introduction of the AP034 did not include the model number on the label. When using an external attenuator with the AP034 Active

17、 Differential Probe, make sure it is labeled “AP034.” Interchanging non-compatible attenuators will not damage the probes; however, the transient response of the measured signals will be significantly in error. In addition to being compatible with the included lead set, the probe input connectors wi

18、ll mate with standard 0.025 in. (0.635 mm) square pins in any rotational orientation. To avoid damaging the input connectors, do not attempt to insert connectors or wire larger than 0.036 in. (0.91 mm) in diameter. Avoid rotating square pins after they are inserted into the input connectors. The inc

19、luded accessories simplify the task of connecting the probe to the test circuit: Use the small (0.5 mm) mini clips with the flexible lead set when connecting to fine-pitch surface mount IC leads. RadioFans.CN 收音机爱 好者资料库 ?ISSUED: January 2000AP034-OM-E Rev D ? The larger (0.8 mm) mini clips can be us

20、ed to connect to through-hole leaded components. The offset round pins can be used for hand-held probing applications. Reposition the pins by rotating them to obtain the required spacing. PROBE INPUT LOADING Attaching any probe to a test circuit will add some loading. In most applications, the high

21、impedance of the AP034 Active Differential Probe inputs imparts an insignificant load to the test circuit. However at very high frequencies, the capacitive reactance of the probes input capacitance may load the circuit enough to affect measurement accuracy. The equivalent model of the probe input ci

22、rcuits is shown below: Figure 1. AP034 Equivalent Input Model GROUNDING THE PROBE The single lead along with one of the larger (0.8 mm) mini clips can be used to ground the probe to the test circuit. Insert the pin end of the lead into the receptacle marked: Note Do not use the attenuator encoding r

23、eceptacle (unmarked socket near the input) to ground the probe. Connecting to the encoding receptacle will not provide adequate grounding, and may result in incorrect scale factor indication. 1 M 1 M 1.5 pF -+ 1.5 pF 0.1 pF AP034-OM-E Rev DISSUED: January 2000? ? In most cases it is not necessary to

24、 ground the probe to the circuit under test. However, if the test circuit is isolated from earth ground, it is usually necessary to connect the probe ground to a point in the circuit. Grounding test circuits that are referenced to earth ground may improve the fidelity of high-frequency components in

25、 the waveforms. The potential for improvement with grounding will vary depending on the common mode source impedance. However, connecting the probe ground to a circuit that is referenced to earth ground can create a ground loop that may add noise to low-amplitude signals*. Rejection of high- frequen

26、cy common mode signals is improved when the probe head is ungrounded. The best recommendation for connecting or not connecting the probe ground is to try both configurations and select the one that performs the best. Note The AP034 Active Differential Probe transmits the measured signal differential

27、ly through the probe cable. This essentially eliminates signal degradation from ground loop effects within the probe. However, creating a ground loop may introduce signal distortions in the test circuit itself, or in any coaxial cable between the ADPPS power supply and the test instrument. ?ISSUED:

28、January 2000AP034-OM-E Rev D ? SELECTING THE PROPER RANGE The AP034 Active Differential Probe has a fixed gain of X1 (unity). Use of the 10 or 20 external attenuators reduces the amplitude of the input signal when it is necessary to extend the dynamic operating range of the probe. Attenuating the in

29、put signal increases both the differential mode range and common mode range of the probe. Refer to the block diagram below. Figure 2. AP034 Block Diagram By using the plug-on attenuator, you can extend the attenuation range to 20. Do not use the 10 and 20 plug-on attenuators simultaneously. The maxi

30、mum ranges are given in the following table: Table 1. AP034 Dynamic ranges and input capacitance at different attenuator settings 1 Attenuation (Probe Only) 10 Attenuation 20 Attenuation Common Mode Range16 V42 V42 V Differential Mode Range *400 mV4 V8 V *Offset moves the center point of this range.

31、 + - X1 50 ControlProbe + VOffs X1 X1 1 - 1 + AP034-OM-E Rev DISSUED: January 2000? ? When using a differential probe or amplifier, be careful to avoid exceeding the common mode range. Because the common mode signal is rejected by the differential probe, and is not displayed, changes in the amplitud

32、e of the common mode component are not apparent to the user. Exceeding the common mode range may introduce distortion into the AP034 output. Circuitry in the probe detects the presence of either attenuator, and displays the effective gain of the probe on the probe front panel. OPERATION WITH LECROY

33、OSCILLOSCOPES When the AP034 probe is connected to a LeCroy oscilloscope equipped with ProBus interface, the displayed scale factor will be adjusted to account for the effective gain of the probe. The channel OFFSET knob will control the probe offset, rather than the offset at the oscilloscope input

34、. The probe control menu can be activated by pressing the COUPLING button while the channel to which the probe is attached is selected. Figure 3. AP034 Probe Control Menu ?ISSUED: January 2000AP034-OM-E Rev D ? When the AP034 Active Differential Probe is first connected to the oscilloscope, the foll

35、owing message will appear: “WARNING: Probe offset buttons are locked.” This alerts you that offset control must be made through the oscilloscope, rather than through the buttons located on the probe. It does not indicate a failure in the probe or oscilloscope. Note: Correct display of scale factor w

36、ith the 20 attenuator installed and correct operation of probe offset require that software version 8.1 or higher be loaded. Refer to the manual section “Oscilloscope Software Compatibility” for additional information. AP034 USE WITH THE ADPPS POWER SUPPLY The optional ADPPS Power Supply allows the

37、AP034 Active Differential Probe to be used with instruments that are not equipped with the ProBus interface. When used with the ADPPS, the AP034 must be terminated into 50 ? input impedance is not 50 ? ? ? ? ? ? ? between the ADPPS and the instrument input. If a coaxial extension cable is used, the

38、terminator should be located at the instrument end of the cable. Note that the additional parasitic losses of extension cables may reduce the usable bandwidth of the system below the AP034 specification. To prevent signal distortion, it is necessary to keep the AP034 output less than 400 mV at all t

39、imes. With the ProBus interface (see note on following page), the oscilloscope OFFSET control actually controls the AP034 offset. Without the ProBus, it is acceptable to use the oscilloscope to position the waveform at high sensitivities, but it is a practice that can lead to erroneous measurements

40、when the probe output exceeds 400 mV. Therefore, when the ADPPS is used, it is preferable to use the AP034 offset function to perform all waveform positioning. The AP034 offset allows you to measure signals up to 2.0 V (1.6 V of offset plus 400 mV of output signal). With accessory plug-on attenuator

41、s, the effective offset is increased, and input signals of 20 V (10) or 40 V (20) may be viewed. The peak AP034-OM-E Rev DISSUED: January 2000? ? signal that can be viewed at any equivalent scale factor is the Input Differential Mode Range plus the offset used. See Adding Offset on the following pag

42、e. When using the AP034 with the ADPPS power supply on oscilloscopes without ProBus interface, use the following table to select the desired effective volts per division and determine the offset available. Table 2. Recommended AP034 and Oscilloscope settings to obtain desired equivalent Volts/Divisi

43、on Equivalent Scale Factor Oscilloscope Scale Factor AP034 Attenuation Common Mode Range Input Differential Mode Range Maximum Offset Maximum Observable Signal with Offset Input Noise (nV/Hz), Typical 2 mV/Div2 mV/Div116V8 mV21.6 V1.608 V35 5 mV/Div5 mV/Div116 V20 mV21.6 V1.620 V35 10 mV/Div10 mV/Di

44、v116 V40 mV21.6 V1.640 V35 20 mV/Div20 mV/Div116 V80 mV21.6 V1.680 V35 50 mV/Div50 mV/Div116 V200 mV21.6 V1.800 V35 100 mV/Div100 mV/Div116 V400 mV31.6 V2.0 V35 200 mV/Div20 mV/Div10142 V800 mV216 V16.8 V350 500 mV/Div50 mV/Div10142 V2 V216 V18 V350 1 V/Div100 mV/Div10142 V4 V316 V20 V350 2 V/Div100

45、 mV/Div20142 V8 V332 V40 V700 1 Attenuation obtained using the external 10 or 20 attenuator. 2 Input differential mode range displayed is limited by 4 divisions of vertical scale on oscilloscope. 3 Limited by probe output and 4 divisions of vertical scale on oscilloscope. Oscilloscope OFFSET and POS

46、ITION must be set to zero. ?ISSUED: January 2000AP034-OM-E Rev D ? ADDING OFFSET The AP034 Active Differential Probe has true differential offset capability. This allows you to remove a DC bias voltage from the differential input signal while maintaining DC coupling. By using probe offset rather tha

47、n the POSITION control on the oscilloscope, the full dynamic range of the probe remains centered around the offset level. Figure 4. Effect of Differential Offset When the AP034 Active Differential Probe is used with a LeCroy oscilloscope equipped with ProBus interface, the probe offset can be contro

48、lled with the channel OFFSET knob.* The buttons on the probe housing will be disabled. When used with the ADPPS Power Supply on instruments that lack ProBus support, offset can be controlled with the buttons on the probes front panel. The offset can be returned to zero at any time by briefly pressing both the ? and ? OFFSET buttons at the same time. Pressing both the ? and ? OFFSET buttons for more than 2 seconds will initiate an Autobalance cycle. *Note Probe offset is controlled with the channel OFFSET knob in oscilloscope software versions 8.1.0