Functions and characteristics

Ultra high impedance input : more than 1013ohm
Ultra low input leakage current : less than 1pA
Broad voltage dynamic range : 20Vp-p
Short rise time : 350ns
Effective for voltage holding ratio measurement of LCD 's (liquid crystal display unit) because of provision 

of SUPPLY INPUT (power source input terminal).

The input terminal is of a 3 terminal structure, and a circuit that compensates for (cancels) insulation resistance and capacitance 

of the measuring cable is equipped with.

The input circuit unit is accommodated in a case controlled at constant low temperature, and the input resistance and input leakage

current characteristics are hardly affected by the ambient temperature.

MZ101 has characteristics of ultra high input resistance and ultra low input leakage current. It is a non-conventional impedance converter of a new type that materializes wide input voltage range and high frequency characteristics. It has the performance that input resistance is more than 1013ohm, input leakage current is within 1pA, measuring input voltage range is 20Vp-p, frequency characteristic is 1MHz and output resistance is 50ohm. Therefore, when MZ101 is applied to the waveform measurement of a high impedance circuit network, it is able to measure without influencing the measuring circuit. Furthermore, a power source terminal for impressing voltage to the input terminal is provided, an electronic switch (FET is used) between both terminals, and switching can be performed by the signal at the switch control terminal. MZ101 exhibits superior power in the measurement and evaluation of electronic parts of high impedance systems such as the measurement of insulation resistance of capacitor and the measurement of voltage holding ratio of LCD.

Theory of operation

MZ101 is composed of FET source follower, buffer amplifier (1) and supply input voltage ON / OFF switch (FET switch). Each FET is of ultra low leakage current, and in addition, devices connected to the input signal line are accommodated in a case controlled at constant low temperature. Therefore, any leakage current is suppressed to a minimum level and variation caused by temperature is minor. Buffer amplifier (1) are inserted for correcting the gain of the FET source follower and for providing output buffer function. The output of buffer amplifier (1) is connected to the inside shield of the input terminal, for the purpose of canceling the influence of the measuring cable.

Applications

1. High impedance circuit network measurement

For high impedance circuit network measurement, the circuit is adversely affected if a probe of the oscilloscope is used because input resistance of the probe is as low as 10Mohm.
When MZ101 is used, however, the measuring system will not be adversely affected because its input resistance is 1013ohm or higher. At this time, connect the HIGH terminal of the measuring cable to the measuring point, LOW terminal to the circuit ground and GUARD terminal to the shielding case insulated from the circuit ground. Furthermore, keep SUPPLY INPUT terminal and CONTROL INPUT terminal open without connecting anything.

2. Capacitor's insulation resistance measurement

Sample hold capacitor and integrator capacitor require low losses, i.e., high insulation resistance. As the method for measurement of insulation resistance (parallel resistance) of a capacitor, place the capacitor to be measured in a shielding case and connect the measuring cable as diagram shown. Connect the DC power source to SUPPLY INPUT terminal and input the TTL level square wave to CONTROL INPUT terminal. In addition, make connection to the digital oscilloscope (DSO) as diagram shown.
While the square wave input to the CONTROL INPUT terminal is of a low level, the internal FET switch is ON, and capacitor Co to be measured is charged to E (V) of the DC power source. When the level is changed to a high level later, the FET switch is OFF and Co begins to discharge. This discharge curve is measured with the DSO. For instance, when voltage V (t) lowered by 20% from E (V), and time t are measured, the insulation resistance can be calculated using a numerical expression.

3. Voltage holding ratio measuring system for LCD

The voltage holding ratio of LCD can be measured by the system composed of MZ101, 

shielding box ME8662N , arbitrary function synthesizer MFG206, A / D board and PC as shown below.

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