Active probe for measuring voltage at high impedances
An active probe (1) for measuring a voltage across a high value impedance, the active probe (1) including: an impedance matching circuit (10) configured to have an input impedance at least 100 times higher than the impedance to be measured, and to deliver a low impedance signal at the output; a probe tip (6) configured to take a measurement and connected to the impedance matching circuit (10); a ground reference (G) connected to the impedance matching circuit (10); the impedance matching circuit (10) including, connected in cascade, at least one input circuit (14) and a non-inverting amplifier circuit (16) adapted to high impedance values.
1 . An active probe for measuring a voltage across a high-value impedance of at least 10 gigaohms (GΩ) of an electronic circuit, said probe comprising:
an impedance matching circuit configured, on the one hand, to have an input impedance at least 100 times higher than the high-value impedance of the electronic circuit on which the voltage is measured and, on the other hand, to deliver a low impedance signal at an output of the impedance matching circuit;
a probe tip configured to take a measurement and connected to said impedance matching circuit;
a ground reference connected to said impedance matching circuit; and
said impedance matching circuit comprising, in a cascade, at least one input circuit and a non-inverting amplifier circuit adapted to high impedance values;
wherein the non-inverting amplifier circuit comprises:
an operational amplifier having inverting and non-inverting inputs;
a resistor arranged at the inverting input of said operational amplifier; and
a guard ring surrounding the inverting and non-inverting inputs of said operational amplifier and, at least partially, the resistor at the inverting input of said operational amplifier.
2 . The probe according to claim 1 , wherein the low impedance output of said impedance matching circuit has an impedance that is equal to or less than 50 ohms.
3 . The probe according to claim 1 , wherein the impedance matching circuit comprises at least one component and/or a filter circuit.
4 . The probe according to claim 1 , wherein said probe is configured to measure a direct current (DC) voltage and/or a voltage having a frequency of less than 60 Hz.
5 . The probe according to claim 1 , wherein the probe is configured to measure the voltage of the electronic circuit having the high-value impedance between 10 gigaohms (GΩ) and 50 gigaohms (GΩ).
6 . The probe according to claim 1 , wherein the impedance matching circuit has a transfer function H(p) including three poles (ω 1-3 ) and a zero (ω z ).
7 . The probe according to claim 6 , wherein the input circuit has an input impedance higher than 50 gigaohms (GΩ).
8 . The probe according to claim 1 , wherein the input circuit comprises a divider bridge.
9 . The probe according to claim 1 , wherein said input circuit comprises at least one other resistor including at least one other guard ring fixed to a body of said at least one other resistor.
10 . The probe according to claim 9 , wherein the at least one other guard ring of said at least one other resistor comprises a stainless steel ring fixed to a middle of the body of the at least one other resistor and a metal braid connecting the at least one other guard ring to a ground.