High speed temperature controlled electrometer

Claim 2

An electrometer for measuring extremely low currents, in the order of ion current levels, comprising: an input and an output, preamplifier means connected to said input and adapted to convert the current applied to said input to a voltage corresponding in value to the value of said input current, sensor means connected to said preamplifier means for sensing the temperature of said preamplifier during its operation, and means connected to said sensor means for controlling the temperature of said preamplifier and sensor means during operation so as to maintain said preamplifier and sensor within a predetermined range of temperature.

Claim 3

The electrometer as claimed in claim 1 wherein said preamplifier means and said sensor means are disposed on thermally conducting substrate means, thermo-electric means, said substrate means being disposed on said thermo-electric means, said sensor means and preamplifier means being responsive to the temperature produced by said thermo-electric means, and said control means being coupled to both said sensor means and said thermo-electric means for maintaining the temperature of said substrate in a predetermined temperature level.

Claim 4

The electrometer as claimed in claim 2 wherein said preamplifier means comprises a first amplifier, a second amplifier and a third amplifier, said first amplifier comprising a pair of JFET transistors, said second amplifier being connected to the output of said first amplifier and comprising a pair of bipolar transistors, and said third amplifier being coupled to said second amplifier and comprising an operational amplifier.

Claim 5

The electrometer as claimed in claim 3 further including an extremely high feedback resistance between the input and the output, said resistance being located on said substrate means and the temperature thereof controlled by said thermo-electric means.

Claim 6

The electrometer as claimed in claim 4 wherein means are provided for maintaining the FET gate leakage current to said first amplifier at a predetermined level.

Claim 7

The electrometer as claimed in claim 5 wherein means are provided for adjusting the gain of said amplifier means.

Claim 8

The electrometer as claimed in claim 6 wherein said means for adjusting the gain comprises a pair of transistors arranged to operate as switches to selectively couple additional resistance means into said circuit and located between said high resistance feedback and said input and output.

Claim 9

The electrometer as claimed in claim 7 wherein said temperature control device comprises a control amplifier means and means for adjusting the current flow from and to said amplifier means so as to adjust the temperature of said thermo-electric means.

Claim 10

The electrometer as claimed in claim 8 wherein the input to said control amplifier means is connected to said temperature sensor and responsive to the current generated thereby due to changes in temperature and wherein the output of said control amplifier means is connected to said thermo-electric means to control the latter's temperature according to the temperature of the sensor means.

Claim 11

The electrometer as claimed in claim 9 wherein said preamplifier means, sensor means, feedback resistance means and thermo-electric means are enclosed in a hermetically sealed housing to protect the enclosed items from humidity and contaminants.

Claim 12

The electrometer as claimed in claim 10 wherein said transistors which are arranged to operate as switches are of the FET type.

Claim 13

The electrometer as claimed in claim 11 wherein all components with said housing are of the microcircuit type with interconnects, the longest of which is 0.1 in. of 0.001 in. in thickness.

Claim 14

The electrometer as claimed in claim 12 wherein said high feedback resistance is in the order of 0.002 in. 2 and an effective shunt capacity of less than 0.01 picofarads.

Claim 15

An electrometer for measuring extremely low currents, comprising: means defining a hollow, hermetically sealed, housing, amplifiier means, temperature sensor means, and means for maintaining the temperature of said preamplifier and sensor means at a preselected level, all enclosed within said housing and responsive to control means for maintaining the amplifier and sensor means at the preselected temperature level.

Claim 16

An electrometer for measuring extremely low currents, comprising: means defining a hollow, hermetically sealed, housing, amplifiier means, temperature sensor means, and means for maintaining the temperature of said preamplifier and sensor means at a preselected level, all enclosed within said housing and responsive to control means for maintaining the amplifier and sensor means at the preselected temperature level.

Claim 17

The electrometer as claimed in claim 14 wherein said control means is separate from said housing.

Claim 18

The electrometer as claimed in claim 15 wherein said control means is coupled to said temperature sensing means and temperature maintaining means for sensing the output signal from said sensor means and producing a signal to be applied to said temperature maintaining means for maintaining the temperature of said temperature maintaining means, amplifier and sensor means at the preselected level.

Claim 19

The electrometer as claimed in claim 16 wherein said control means include means for adjusting the gain of said amplifier.

Claim 20

The electrometer as claimed in claim 17 wherein said control means includes an operational amplifier, variable resistance means connected to one input to said amplifier and to a voltage source, the output of said sensor means also being connected to said one input so that the signal from said sensor means and the signal from said variable resistance means are summed and compared with a third signal source by said operational amplifier, the output of which is then directed to said temperature maintaining means.

Claim 21

An electrometer for measuring extremely low currents in the order of ion current levels, comprising: an input and an output, a preamplifier means including JFET transistors connected to said input and adapted to convert the current applied to said input to a voltage corresponding in value to the value of said input current, sensor means for sensing the temperature of preamplifier during its operation, means for controlling the temperature of said preamplifier and sensor means during operation so as to maintain said preamplifier and sensor within a predetermined range of temperature, preferably at operating temperatures less than the environment operating temperature, a thermally conducting substrate, said preamplifier means being disposed on said substrate, thermo-electric means, said substrate being disposed on said thermo-electric means so that said sensor means and preamplifier are responsive to the temperature of said thermo-electric means, and said control means being coupled to both said sensor means and said thermo-electric means for maintaining the temperature of the substrate within a small preselected temperature level, an extremely high feedback resistance between said input and said output and located on said substrate, said feedback resistor utilizing resistive materials which enable its size to be extremely small thereby providing extremely small effective shunt capacity promoting its fast response characteristics, said control means being coupled to both said sensor means and said thermo-electric means for maintaining the temperature of the substrate to maintain the FET gate leakage small and to hold the resistance value of said feedback resistance within a predetermined range so that input ion current levels may be measured.

Claim 22

An electrometer for measuring extremely low currents in the order of ion current levels, comprising: an input and an output, a preamplifier means including JFET transistors connected to said input and adapted to convert the current applied to said input to a voltage corresponding in value to the value of said input current, sensor means for sensing the temperature of preamplifier during its operation, means for controlling the temperature of said preamplifier and sensor means during operation so as to maintain said preamplifier and sensor within a predetermined range of temperature, preferably at operating temperatures less than the environment operating temperature, a thermally conducting substrate, said preamplifier means being disposed on said substrate, thermo-electric means, said substrate being disposed on said thermo-electric means so that said sensor means and preamplifier are responsive to the temperature of said thermo-electric means, and said control means being coupled to both said sensor means and said thermo-electric means for maintaining the temperature of the substrate within a small preselected temperature level, an extremely high feedback resistance between said input and said output and located on said substrate, said feedback resistor utilizing resistive materials which enable its size to be extremely small thereby providing extremely small effective shunt capacity promoting its fast response characteristics, said control means being coupled to both said sensor means and said thermo-electric means for maintaining the temperature of the substrate to maintain the FET gate leakage small and to hold the resistance value of said feedback resistance within a predetermined range so that input ion current levels may be measured.