Feed-forward operational amplifier noise cancellation technique and associated filter and delta-sigma modulator

Patent metadata

Field	Value
Publication number	US-9929742-B2
Application number	US-201715652207-A
Country	US
Kind code	B2
Filing date	Jul 17, 2017
Priority date	Aug 17, 2016
Publication date	Mar 27, 2018
Grant date	Mar 27, 2018

Abstract

A circuit includes a first amplifying stage, a noise extraction circuit and a noise cancellation circuit. The first amplifying stage is arranged for receiving an input signal to generate an amplified input signal. The noise extraction circuit is coupled to the first amplifying stage, and is arranged for receiving at least the amplified input signal to generate a noise signal associated with noise components of the amplified input signal. The noise cancellation circuit is coupled to the first amplifying stage and the noise extraction circuit, and is arranged for cancelling noise components of the amplified input signal by using the noise signal generated by the noise extraction circuit, to generate a noise-cancelled amplified input signal.

First claim

What is claimed is:

1. A circuit, comprising:
a first amplifying stage, for receiving an input signal to generate an amplified input signal;
a noise extraction circuit, coupled to the first amplifying stage, for receiving at least the amplified input signal to generate a noise signal associated with noise components of the amplified input signal, wherein the noise extraction circuit does not generate a signal component of the input signal or the amplified input signal; and
a noise cancellation circuit, coupled to the first amplifying stage and the noise extraction circuit, for cancelling noise components of the amplified input signal by using the noise signal generated by the noise extraction circuit, to generate a noise-cancelled amplified input signal.

2. The circuit of claim 1 , wherein the noise extraction circuit generates the noise signal that is equivalent to the noise components of the amplified input signal.

3. The circuit of claim 1 , wherein the amplified input signal and the noise signal are current signals, and the circuit further comprising:
a second amplifying stage, wherein the second amplifying stage comprises an operational amplifier, and input nodes of the operational amplifier receives the amplified input signal and the noise signal to obtain the noise-cancelled amplified input signal.

4. The circuit of claim 1 , wherein a gain of the first amplifying stage is greater than one.

5. The circuit of claim 1 , wherein noise extraction circuit receives the input signal and the amplified input signal to generate a noise signal, and the first amplifying stage comprises:
an operational amplifier;
an input network circuit, wherein the operational amplifier receives the input signal via the input network circuit; and
a feedback network circuit, coupled between input terminals and output terminals of the operational amplifier; and
the noise extraction circuit comprises:
an auxiliary operational amplifier;
a scaled input network circuit, wherein the auxiliary operational amplifier receives the input signal via the scaled input network circuit;
a first scaled feedback network circuit, coupled between input terminals and output terminals of the auxiliary operational amplifier; and
a second scaled feedback network circuit, wherein the auxiliary operational amplifier receives the amplified input signal via the second scaled feedback network circuit.

6. The circuit of claim 5 , wherein the auxiliary input network circuit and the input network circuit have same circuit structure with different sizes, and the first auxiliary feedback network circuit and the feedback network circuit have same circuit structure with different sizes.

7. The circuit of claim 6 , wherein a size ratio between the input network circuit and the auxiliary input network circuit is the same as a size ratio between the feedback network circuit and the first auxiliary feedback network circuit.

8. The circuit of claim 5 , wherein the first auxiliary feedback network circuit and the second auxiliary feedback network circuit are the same.

9. The circuit of claim 5 , wherein the input signal comprises a first input signal and a second input signal serving as a differential pair, the first input signal is inputted into a positive input terminal of the operational amplifier, and the second input signal is inputted into a negative input terminal of the operational amplifier via the input network circuit; and the first input signal is inputted into a negative input terminal of the auxiliary operational amplifier, and the second input signal is inputted into a positive input terminal of the auxiliary operational amplifier via the auxiliary input network circuit.

10. The circuit of claim 9 , wherein the amplified input signal comprises an amplified first input signal and an amplified second input signal, the amplified first input signal is inputted into the positive input terminal of the auxiliary operational amplifier, and the amplified second input signal is inputted into the negative input terminal of the auxiliary operational amplifier via the second auxiliary feedback network circuit.

11. The circuit of claim 5 , wherein the circuit is applied to a filter with programmable gain amplifier.

12. The circuit of claim 1 , wherein noise extraction circuit a current signal extracted from the input signal and the amplified input signal to generate a noise signal, and the first amplifying stage comprises:
an operational amplifier, for receiving the input signal;
a feedback network circuit, coupled between input terminals and output terminals of the operational amplifier; and
the noise extraction circuit comprises:
an auxiliary operational amplifier;
a first scaled feedback network circuit, coupled between input terminals and output terminals of the auxiliary operational amplifier; and
a second scaled feedback network circuit, wherein the auxiliary operational amplifier receives the current signal via the second scaled feedback network circuit.

13. The circuit of claim 12 , wherein the auxiliary input network circuit and the input network circuit have same circuit structure with different sizes, and the first auxiliary feedback network circuit and the feedback network circuit have same circuit structure with different sizes.

14. The circuit of claim 12 , wherein the first auxiliary feedback network circuit and the second auxiliary feedback network circuit are the same.

15. The circuit of claim 12 , wherein the circuit is applied to a delta-sigma modulator.

16. A filter with programmable gain amplifier, comprising:
a first amplifying stage, for receiving an input signal to generate an amplified input signal;
a noise extraction circuit, coupled to the first amplifying stage, for receiving at least the amplified input signal to generate a noise signal associated with noise components of the amplified input signal; and
a noise cancellation circuit, coupled to the first amplifying stage and the noise extraction circuit, for cancelling noise components of the amplified input signal by using the noise signal generated by the noise extraction circuit, to generate a noise-cancelled amplified input signal.

17. The filter of claim 16 , wherein the noise extraction circuit generates the noise signal that is equivalent to the noise components of the amplified input signal, and the noise extraction circuit does not generate signal components of the input signal or the amplified input signal.

18. A delta-sigma modulator, comprising:
a receiving circuit, for receiving an input signal and a feedback signal to generate a subtraction signal;
a loop filter, coupled to the receiving circuit, for receiving the subtraction signal to generate a filtered subtraction signal;
a quantizer, coupled to the loop filter, for generating a digital output signal according to the filtered subtraction signal; and
a feedback circuit, for receiving the digital output signal to generate the feedback signal;
wherein the loop filter comprises:
a first amplifying stage, for receiving the subtraction signal to generate an amplified subtraction signal;
a noise extraction circuit, coupled to the first amplifying stage, for receiving at least the amplified subtraction signal to generate a noise signal associated with noise components of the amplified subtraction signal; and
a noise cancellation circuit, coupled to the first amplifying stage and the noise extraction circuit, for cancelling noise components of the amplified subtraction signal by using the noise signal generated by the noise extraction circuit, to gen

Assignees

• Mediatek Inc

Inventors

• Tsai Hung-Chieh

Classifications

• H03M3/436

  characterised by the order of the loop filter, e.g. error feedback type · CPC title

• H03F2203/45116

  Feedback coupled to the input of the differential amplifier · CPC title

• H03F1/26 Primary

  Modifications of amplifiers to reduce influence of noise generated by amplifying elements · CPC title

• H03M3/458

  Analogue/digital converters using delta-sigma modulation as an intermediate step · CPC title

• H03M3/368 Primary

  of noise other than the quantisation noise already being shaped inherently by delta-sigma modulators · CPC title