Circuit and method for a high common mode rejection amplifier by using a digitally controlled gain trim circuit

Patent metadata

Field	Value
Publication number	US-10250210-B2
Application number	US-201615201941-A
Country	US
Kind code	B2
Filing date	Jul 5, 2016
Priority date	Jul 5, 2016
Publication date	Apr 2, 2019
Grant date	Apr 2, 2019

Abstract

An amplifier comprising a differential amplifier configured to be provide a comparator function, and a gain trimming circuit is electrically configured to provide gain trimming using a T-network comprising a varistor element. In addition, a method of trimming the gain of a differential amplifier, comprising the steps of a first step, (a) providing the differential amplifier comprising resistors in both of its paths, a second step, (b) providing a varistor in a T-network between both said paths; and lastly, a third step, (c) trimming the gain of the differential amplifier by adjusting the varistor's resistance.

First claim

What is claimed is:

1. A differential amplifier with high common mode rejection, comprising:
resistors in both paths of said differential amplifier wherein said differential amplifier comprises a pair of said resistors in each of its feedback paths; and
a varistor in a T-network between said both said feedback paths, to provide gain trimming; and

wherein said varistor is connected between each pair of said resistors.

2. The differential amplifier of claim 1 , wherein said differential amplifier comprises a pair of said resistors in each of its input paths, wherein said varistor in a T-network is connected between said input paths.

3. The differential amplifier of claim 1 wherein an input switch is connected to each input path of said differential amplifier, before an input resistor, and is configured to connect said input path to an input reference voltage during said gain trimming.

4. The differential amplifier of claim 3 , wherein a feedback switch is connected to each feedback path of said differential amplifier, on the output terminals of said differential amplifier, and is configured to connect said feedback path to a voltage Vmid during said gain trimming.

5. The differential amplifier of claim 4 , wherein an output switch is connected between each output of said differential amplifier and said output terminal of each feedback path, and is configured to disconnect said differential amplifier outputs during said gain trimming.

6. The differential amplifier of claim 1 , further comprising a comparator connected to output terminals of said differential amplifier, wherein said comparator is configured to compares the output signals of said differential amplifier.

7. The differential amplifier of claim 1 , further comprising a comparator connected to input terminals of said differential amplifier, wherein said comparator is configured to compare said input terminals of said differential amplifier.

8. A method of trimming gain of a differential amplifier, comprising the steps of:
(a) wherein said a differential amplifier comprises resistors in both of its paths wherein said differential amplifier comprises a pair of said resistors in each of its feedback paths;
(b) connecting a varistor in a T-network between both said feedback paths, wherein said varistor is connected between each pair of said resistors;
(c) trimming the gain of said differential amplifier by adjusting resistance of said varistor.

9. The method of trimming gain of the differential amplifier of claim 8 , further comprising to provide a relationship between input impedance mismatch (mm s ) and feedback impedance mismatch (mm f ).

10. The method of trimming gain of the differential amplifier of claim 9 , when the gain trim setting, x, is 0.5, there is no mismatch.

11. The method of trimming gain of the differential amplifier of claim 10 , where said gain trimming setting, x, is further evaluated from the following system of equations wherein Adiff 1 and Adiff 2 are gain of the differential amplifier, A is amplification, and a, b, and c are standard polynomial of gain trimming setting x:

A

diff
⁢

⁢
1

=

R

f
⁢

⁢
1

⁢

R

f
⁢

⁢
2

R
s

⁢

R
T

⁢

⁢
trim

+

R

f
⁢

⁢
1

⁢

+

R

f
⁢

⁢
2

R
s

Equation
⁢

⁢
1

A

diff
⁢

⁢
2

=

R

f
⁢

⁢
1

′

⁢

R

f
⁢

⁢

Assignees

• Dialog Semiconductor Uk Ltd

Inventors

• Mengad Zakaria
• Collins Steven
• Vasilev Vladislav

Classifications

• H03F3/45928

  using IC blocks as the active amplifying circuit · CPC title

• H03F2203/45042

  One or more resistors are added or changed as balancing to reduce the offset of the dif amp · CPC title

• H03F2203/45534

  the FBC comprising multiple switches and being coupled between the LC and the IC · CPC title

• H03F2203/45044

  One or more switches are opened or closed to balance the dif amp to reduce the offset of the dif amp · CPC title

• H03F2203/45591

  the IC comprising one or more potentiometers · CPC title