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- 200 MHz
- 10m cable
- Galvanically isolated measurement solution for accurately resolving high bandwidth, differential signals in the presence of large common mode voltages
- Best in class common mode rejection performance across bandwidth
- Output clamping
- Class I laser
- Bandwidth/Rise time (typical): 200 MHz / ≤ 1.8 ns
- Half/Full bridge designs using GaN, SiC, IGBTs
- Floating measurements
- Power converter design
- Power device evaluation
- Switching power supply design
- Inverter design
- Motor drive design
- Electronic ballast design
- Current shunt measurements
- Remote probing capability
Isolated Differential Probe Measurement System
The Tektronix TIVM02L Isolated Differential Probe Measurement System, 200 MHz, IsoVu, 10m Cable can be used on most Tektronix oscilloscopes with the TekVPI interface, and on the MSO/DPO70K series of oscilloscopes with the TCA-VPI50 adapter.
TIVM02L utilizes an electro-optic sensor that converts the electrical signal from the sensor tip cables to an optical signal, which electrically isolates the device-under-test from the oscilloscope; it incorporates four separate lasers, an optical sensor, five optical fibers, and sophisticated feedback and control techniques. The sensor head, which connects to the test point, has complete electrical isolation and is powered over one of the optical fibers (no batteries required).
TIVM02L is an ideal solution for users making the following measurements:
- Differential measurements in the following conditions:
- Complete galvanic isolation is required
- High common mode voltage
- High frequency common mode interference
- High frequency measurements
- Measurements in high EMI environments
- EMI compliance testing
- ESD testing
Measurement Pain Points and Sources of Error
The objective of the differential measurement is to get a perfect representation of VA-B as shown in Figure 1. Unfortunately, the perfect representation of VA-B is not possible due to some of the following causes:
- Common mode voltage or common mode interference
- Radiated emissions
- Ground loops
- Measurement system inaccuracy:
- Insufficient bandwidth
- Insufficient common mode rejection capabilit
- Insufficient sensitivity
Voltage Derating Over Frequency
All differential probes have a common mode voltage rating with some probes specifying a common mode voltage range of thousands of volts. However, the listed specification is generally true only at DC and low frequencies. The probe’s common mode voltage capability is derated as the frequency of the signal increases, which severely limits the common mode voltage capability at higher frequencies.
An example of this derating is the common mode voltage plot of Keysight’s N2890A 100 MHz high voltage differential probe shown in Figure 2. Although the voltage rating of the probe is 1 kVrms at low frequencies, the probe’s capabilities start to roll off at 2 MHz and this probe is only capable of 20 Vrms at 100 MHz. This is a limitation that is rarely understood and users often fail to realize that a probe such as this one with a 1 kVrms rating is only capable of 20 Vrms at maximum bandwidth. This misunderstanding can result in measurement inaccuracy and damaged equipment.
CMRR Derating over Frequency
CMRR Derating over Frequency Common-mode rejection ratio (CMRR) is a differential probe's ability to reject any signal that is common to both test points in a differential measurement (VA – VB). CMRR is a key figure of merit for differential probes and amplifiers, and it is defined by:
CMRR = | ADiff / ACM |
ADiff = the voltage gain for the difference signal
ACM = the voltage gain for common-mode signal
Ideally, ADiff should be large and ACM would be zero, resulting in an infinite CMRR. In practice, a CMRR of at least -80 dB (10,000:1) is considered quite good. An amplifier that has long been considered best in class is the LeCroy DA1855A. In Figure 3, the DA1855A's CMRR exceeds the -80 dB level at low frequencies up to a few MHz. However, the CMRR capability of this amplifier quickly derates and is only capable of a mere -20 dB or 10:1 at 100 MHz. What this means is that a common-mode input signal of 10 volts at 100 MHz will induce a 1 V error signal in the differential measurement. It should be noted that the plot in Figure 3 is for the amplifier only. When using "matched" probes with the amplifier the performance is further degraded.
Common Mode Loading Derating Over Frequency
Although the common mode DC input impedance of a typical probe can be very high, as the signal frequency increases the common mode impedance is dominated by the common mode capacitance to ground. At higher frequencies, the capacitive loading becomes a matter of increasing concern by distorting the waveform and increasing the load on the DUT. As shown in Figure 4, the Keysight N2819A probe has a large common mode input impedance at DC and low frequencies but the impedance drops to 40 Ohms at 1 GHz.
Users need to pay careful attention to all three of these factors which can have a negative impact on the measurement results. The ideal measurement system would not have these limitations and deratings described above.
The TIVM02L Solution to the Common Mode Problem
TIVM02L Common Mode Voltage
TIVM02L architecture with galvanic isolation provides common mode withstand voltages of > 2000 Vpeak across its frequency range with NO derating. The electrical limitation for an optically isolated solution such as TIVM02L is many thousands of volts given TIVM02L's 10 meter fiber optic length. Because TIVM02L achieves galvanic isolation through its fiber optic connection, the only limitation in its common mode voltage rating is due to safety certification standards. Where the Keysight N2790A plot shows degraded performance over frequency, TIVM02L has no derating over frequency.
TIVM02L achieves exceptional CMRR over the entire operating range due to the combination of complete galvanic isolation and its TIVM02L sensor head architecture. It should be noted that the data in Figure 6 is representative of the actual measured CMRR because the measurement was limited by the sensitivity of the test system and the noise floor of the VNA. For comparison, the LeCroy DA1855A without probes at 100 MHz has a CMRR value of 20 dB (10:1) while TIVM02L offers 120 dB (1 Million:1).
TIVM02L Common Mode Loading
Since the TIVM02L system has no electrical connection from the sensor head to ground or the rest of the test system, the only common mode loading is the parasitic capacitance from the sensor head to the environment. For example, placing the sensor head 6 in. (15.25 cm) above a reference plane would result in ~2 pF of parasitic capacitance between the sensor head and the reference plane.
TIVM02L Theory of Operation
TIVM02L utilizes an electro-optic sensor to convert the input signal to optical modulation, which electrically isolates the device-under-test from the oscilloscope. TIVM02L incorporates four separate lasers, an optical sensor, five optical fibers, and sophisticated feedback and control techniques. The sensor head, which connects to the test point, has complete electrical isolation and is powered over one of the optical fibers. Figure 7 shows the block diagram.
The Controller connects to the scope via a coax cable and TekVPI Comp Box. The Controller is powered directly from the TekVPI Interface. The Controller Box provides the following functions:
- TekVPI Interface communication/power link with host oscilloscope
- Microcontroller and support circuitry
- Power Over Fiber laser/driver
- Signal Laser, signal laser driver (adjustable output power) and thermo-electric cooler driver
- Optical Communication (RX/TX)
- Transimpedance Amplifier (TIA) and supporting circuitry
The Sensor Head contains an electrical-to-optical sensor that converts the electrical signal from the DUT to an optical signal to be sent to the controller via the optical fiber link. The Sensor Head also contains a DC/LF feedback loop that measures the DUT signal and sends it to the controller for analysis. This allows the system to correct for a variety of drifts and offset errors in the system. The Sensor Head is powered by an optical link.
The Tip Cables connect the DUT to the sensor head. A variety of Tip Cables with different attenuations will be provided and the customer will select which attenuation to use based on the signal being measured. The Tip Cable will connect to the Sensor Head via an SMA connector. Each tip cable will include readout encoding that allows the Sensor Head to communicate the attenuation factor to the scope to display the correct vertical scale factor.
Five different tip cables will be available with attenuation ranges from 1X to 50X and corresponding differential ranges from +/- 1V to +/- 50V. Since the sensor head input is a 50 Ohm SMA connector, users can connect directly to the sensor head with an SMA cable with a differential range of +/- 1V. This input structure affords users the opportunity to build custom interfaces to the DUTs.
TIVM02L Connectivity Options
Traditional high voltage differential solutions ship with robust accessories such as alligator clips or hook clips that have been suitable for higher voltage environments but have the trade-off of lower signal fidelity. With increasing power densities and higher performance requirements, traditional accessories have become less useful. TIVM02L offers multiple connectivity options to maximize both performance and convenience.
A reference design that can accommodate an MMCX connector as a test point will get the greatest performance and convenience using the TIVM02L solution. With an MMCX connector at the end of the tip cable, TIVM02L will easily snap into MMCX connectors on a reference design board as shown in Figure 9. With a reference design that cannot accommodate an MMCX connector, the TIVM02L measurement solution includes square pin adapters which will fit over square pins soldered onto the test board.
|TIVM02||Tektronix TIVM02 Isolated Differential Probe Measurement System, 200 MHz, IsoVu, 3m Cable||
|TIVM05||Tektronix TIVM05 Isolated Differential Probe Measurement System, 500 MHz, IsoVu, 3m Cable||
|TIVM05L||Tektronix TIVM05L Isolated Differential Probe Measurement System, 500 MHz, IsoVu, 10m Cable||
|TIVM1||Tektronix TIVM1 Isolated Differential Probe Measurement System, 1 GHz, IsoVu, 3m Cable||
|TIVM1L||Tektronix TIVM1L Isolated Differential Probe Measurement System, 1 GHz, IsoVu, 10m Cable||
|Data Sheet:||(246 KB)|