TRANSIMPEDANCE AMPLIFIERS FOR ULTRASONIC SENSING APPLICATIONS

• US 20200136565A1
• Filed: 12/06/2018
• Published: 04/30/2020
• Est. Priority Date: 10/25/2018
• Status: Active Application

• Current Assignee: Analog Devices Global Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices Global Unlimited Company (Analog Devices, Inc.)
• Inventors: TUMATI, Sanjay, AGRAWAL, Vinayak, CLEARY, John A.
• Granted Patent: US 10,848,107 B2
• Time in Patent Office: Days
• CPC Class Codes: B06B 1/06 operating with piezoelectric effect or with electrostriction piezoelectric or electrostrictive devices per se H10N30/00
• CPC Class Codes: B06B 1/0644 using a single piezoelectric element B06B1/0688 takes precedence
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: H03F 1/086 with FET's
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 1/301 in MOSFET amplifiers H03F1/303, H03F1/305, H03F1/308 take precedence
• CPC Class Codes: H03F 1/523 for amplifiers using field-effect devices H03F1/526 takes precedence
• CPC Class Codes: H03F 2200/426 the amplifier comprising circuitry for protection against overload
• CPC Class Codes: H03F 2200/72 the amplifier stage being a common gate configuration MOSFET
• CPC Class Codes: H03F 3/211 using a combination of several amplifiers H03F3/60 takes precedence
• CPC Class Codes: H10N 30/302 Sensors
• CPC Class Codes: H10N 30/802 Circuitry or processes for operating piezoelectric or electrostrictive devices not otherwise provided for, e.g. drive circuits

Abstract

Various transimpedance amplifier (TIA) arrangements for ultrasonic front-end receivers used in ultrasonic sensing applications are disclosed. An example TIA includes three common-source gain stages in a feedback loop with a common-gate stage. In some aspects, the TIA may include a level shifter configured to maintain the voltage at the gate of a transistor used to implement the first common-source gain stage of the feedback loop shifted by a certain amount with respect to the voltage at an input port to the TIA. In some aspects, at least portions of the TIA may be biased using bias currents that are configured to be process-, supply voltage-, and/or temperature-dependent. Various embodiments of the TIAs disclosed herein may benefit from one or more of the following advantages: reduced noise, reduced input impedance, reduced temperature coefficient of input impedance, and stability for a wide range of sensor frequencies.

Claims

1. A transimpedance amplifier (TIA) of an ultrasonic front-end receiver, the TIA configured to convert an input current applied to an input port of the TIA to an output voltage, the input current indicative of a current generated by a piezoelectric transducer (PZT), the TIA comprising:

a first transistor configured to receive the input current at a source terminal of the first transistor;

a second transistor having a drain terminal coupled to a gate terminal of the first transistor;

a third transistor having a drain terminal coupled to a gate terminal of the second transistor; and

a fourth transistor having a drain terminal coupled to a gate terminal of the third transistor.

2. The TIA according to claim 1, wherein a gate terminal of the fourth transistor is coupled to a current source from which the first transistor is configured to receive the input current.

3. The TIA according to claim 2, wherein the current source from which the first transistor is configured to receive the input current is a piezoelectric sensor.

4. The TIA according to claim 2, further comprising a level shifter that includes:

a resistor element coupled between the gate terminal of the fourth transistor and the input port of the TIA, and

a bias current source coupled to the gate terminal of the fourth transistor.

5. The TIA according to claim 4, further comprising:

a capacitor coupled between the gate terminal of the fourth transistor and the input port of the TIA.

6. The TIA according to claim 2, further comprising:

a variable resistor element coupled between the input port of the TIA and a ground potential.

7. The TIA according to claim 6, wherein the variable resistor element is coupled with a capacitor element.

8. The TIA according to claim 6, wherein the gate terminal of the third transistor is coupled to a variable capacitor element.

9. The TIA according to claim 1, further comprising a bias current source configured to generate a bias current for biasing the fourth transistor, where the bias current is dependent on one of more of process variations, supply voltage variations, and temperature variations.

10. The TIA according to claim 1, further comprising an overload protection circuit configured to limit the input current applied to the input port of the TIA to a value that does not exceed a maximum threshold value.

11. The TIA according to claim 1, wherein the first transistor is a common-gate transistor.

12. The TIA according to claim 1, wherein each of the second transistor, the third transistor, and the fourth transistor is a common-source transistor.

13. The TIA according to claim 1, wherein a source terminal of each of the second transistor, the third transistor, and the fourth transistor is coupled to a ground potential.

14. The TIA according to claim 1, wherein the TIA is configured to provide the output voltage at a drain terminal of the first transistor.

15. An ultrasonic sensor system, comprising:

an ultrasonic receiver, configured to;

receive (RX) an RX ultrasonic signal, the RX ultrasonic signal comprising at least a portion of a transmitted (TX) ultrasonic signal that has interacted with an object, where the TX ultrasonic signal is an ultrasonic signal transmitted by an ultrasonic transmitter configured to transmit the TX ultrasonic signal so that the TX ultrasonic signal interacts with the object, and

generate a first electrical signal that is indicative of the RX ultrasonic signal; and

a transimpedance amplifier (TIA) comprising a plurality of common-source amplifiers in feedback with a common-gate amplifier, configured to convert the first electrical signal generated by the ultrasonic receiver to a second electrical signal.

16. The ultrasonic sensor system according to claim 15, wherein the system comprises a plurality of pixels, each of the plurality of pixels comprising a respective ultrasonic receiver.

17. The ultrasonic sensor system according to claim 16, wherein the system comprises a respective TIA at least for one or more of the plurality of pixels.

18. The ultrasonic sensor system according to claim 16, wherein the TIA is configured to convert the first electrical signal generated by two or more of the plurality of pixels.

19. The ultrasonic sensor system according to claim 15, wherein the ultrasonic receiver is a piezoelectric sensor.

20. The ultrasonic sensor system according to claim 15, wherein the system is a fingerprint sensing system.