# US 12,216,143 B2 · Voltage current conversion device

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- Number: US 12,216,143 B2
- Document ID: US12216143B2
- Status: Granted
- Kind: B2
- Application number: 17/911,253
- Filed: 2020-03-18
- Published: 2023-04-13
- Granted: 2025-02-04
- Earliest claimed: 2020-03-18
- Assignees: Nippon Telegraph and Telephone Corporation
- Applicants: Nippon Telegraph and Telephone Corporation
- Inventors: Masayuki Hashisaka; Koji Muraki; Takafumi Akiho
- Web page: https://patentgrep.com/patent/US12216143B2

## CPC

- G01R 19/0092: {Measuring current only}
- H03F 1/34: Negative-feedback-circuit arrangements with or without positive feedback (H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence {; for rejection of common mode signals H03F3/45479})
- G01R 19/0023: {Measuring currents or voltages from sources with high internal resistance by means of measuring circuits with high input impedance, e.g. OP-amplifiers (electrostatic instruments G01R5/28; measuring electrostatic potential G01R15/165; measuring electrostatic fields G01R29/12; amplifiers per se H03F)}
- G01R 19/32: Compensating for temperature change
- H03F 1/223: {with MOSFET's}
- H03F 1/483: {with field-effect transistors}
- H03F 3/04: with semiconductor devices only
- H03F 2200/54: Two or more capacitor coupled amplifier stages in cascade
- H10D 30/47: having two-dimensional [2D] charge carrier gas channels, e.g. nanoribbon FETs or high electron mobility transistors [HEMT]
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H03F: AMPLIFIERS
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

When a current-to-voltage converter is used at low temperatures, the frequency band of measurable small currents is limited. Stray capacitance of a coaxial cable that takes out an output voltage of the current-to-voltage converter from inside to outside a cooling device narrows the operating frequency band of the current-to-voltage converter. The current-to-voltage converter of the present disclosure uses elements exclusively optimized for low-temperature operation (e.g., HEMTs) as electronic elements for current-to-voltage conversion. This configuration realizes current-to-voltage conversion characteristics with significantly more excellent sensitivity than that of the conventional technique even when the current-to-voltage converter is operated at a low temperature of 150K or less or in cryogenic temperature conditions close to absolute zero. Further, a source follower circuit is added to an output stage of the current-to-voltage conversion circuit to isolate the effect of stray capacitance added to the output side of the current-to-voltage conversion circuit and achieve a wider bandwidth.

## Claims

### Claim 1

A current-to-voltage converter comprising:
an amplification unit having at least three stages each including a field-effect transistor (FET), a target current being fed to a first stage, a final stage constituting a source follower configured to feed back an output signal to the first stage, the amplification unit being configured to convert the target current to a voltage; and
a buffer unit that is connected to the amplification unit, constitutes a source follower including a FET, and is configured to output the converted voltage,
wherein each FET is adapted to operation at a temperature of 150 K or less.

### Claim 2 (depends on 1)

The current-to-voltage converter according to claim 1, wherein
the amplification unit has four common source voltage amplifier stages.

### Claim 3 (depends on 1)

The current-to-voltage converter according to claim 1, wherein
each FET is a high electron mobility transistor (HEMT), and has a gate insulating layer is 100 nm or less.

### Claim 4 (depends on 3)

The current-to-voltage converter according to claim 3, wherein
the HEMT is a HEMT with a GaAs—AlGaAs modulation-doped superlattice structure, a pseudomorphic HEMT, or an InP-based HEMT.

### Claim 5 (depends on 1)

A small current measurement device comprising the current-to-voltage converter according to claim 1, the current-to-voltage converter being provided within a cooling device.

### Claim 6 (depends on 2)

The current-to-voltage converter according to claim 2, wherein
each FET is a high electron mobility transistor (HEMT), and has a gate insulating layer is 100 nm or less.

### Claim 7 (depends on 2)

A small current measurement device comprising the current-to-voltage converter according to claim 2, the current-to-voltage converter being provided within a cooling device.

### Claim 8 (depends on 3)

A small current measurement device comprising the current-to-voltage converter according to claim 3, the current-to-voltage converter being provided within a cooling device.

### Claim 9 (depends on 4)

A small current measurement device comprising the current-to-voltage converter according to claim 4, the current-to-voltage converter being provided within a cooling device.