Sigma-delta analog to digital converter

• US 5,392,039 A
• Filed: 05/21/1992
• Issued: 02/21/1995
• Est. Priority Date: 06/01/1991
• Status: Expired due to Fees

• Current Assignee: Marconi Mobile Limited (Leonardo S.p.A.)
• Original Assignee: GEC Marconi Limited (Gooding Consumer Electronics Ltd.)
• Inventors: Thurston, Andrew M.
• Primary Examiner(s): Young, Brian K.
• Application Number:
  US07/886,588
• Time in Patent Office: 1,006 Days
• Field of Search: 341/155, 341/143, 375/26, 375/27, 333/172, 333/175, 333/167
• US Class Current: 341/143
• CPC Class Codes: H03M 3/358 of non-linear distortion, e.g. instability avoiding instability by structural design H03M3/44
• CPC Class Codes: H03M 3/408 by the use of an LC circuit
• CPC Class Codes: H03M 3/43 the quantiser being a single bit one
• CPC Class Codes: H03M 3/454 with distributed feedback, i.e. with feedback paths from the quantiser output to more than one filter stage

Abstract

An analog-to-digital converter has an input for receiving analog signals, a quantizer for producing a digital output of the converter, a first combining node for combining the analog input with a first feedback signal derived from the digital output and producing a first combined signal, and filter circuitry for filtering the first combined signal. The filter circuitry includes at least one filter circuit stage which is not connected to a phase-modifying resistance, and a second combining node for combining an output from the at least one filter circuit stage with a second feedback signal derived from the digital output, and produces a signal for input to the quantizer.

Claims

1. An analog-to-digital converter having an input for receiving analog signals, the converter comprising:

quantizing means for producing a digital output of the converter;

first combining means for combining the analog input with a first feedback signal derived from the digital output and producing a first combined signal; and

filter means for filtering the first combined signal, the filter means including;

at least two filter circuit stages each comprising a parallel resonant circuit which is not connected to a respective phase-modifying series resistive means; and

second combining means for combining an output from the filter means after a final filter circuit stage of the filter means with a second feedback signal derived from the digital output,

said filter means producing a signal for input to the quantizing means;

wherein said second combining means comprises a summing node.

2. An analog-to-digital converter as claimed in claim 1 wherein the at least one filter circuit stage of the filter means is a first stage of the filter means.

3. An analog-to-digital converter having an input for receiving analog signals, the converter comprising:

quantizing means for producing a digital output of the converter;

first combining means for combining the analog input with a first feedback signal derived from the digital output and producing a first combined signal; and

filter means for filtering the first combined signal, the filter means including;

at least one filter circuit stage which is not connected to phase-modifying resistive means; and

second combining means for combining an output from the at least one filter circuit stage with a second feedback signal derived from the digital output,

said filter means producing a signal for input to the quantizing means;

wherein the filter means includes two filter circuit stages each stage comprising;

parallel resonant circuits without series resistive means, and

a buffer circuit,

wherein respective output signals of each stage are combined by said second combining means with respective feedback signals derived from the digital output at the outputs of the respective buffers.

4. An analog-to-digital converter having an input for receiving analog signals, the converter comprising:

quantizing means for producing a digital output of the converter;

first combining means for combining the analog input with a first feedback signal derived from the digital output and producing a first combined signal; and

filter means for filtering the first combined signal, the filter means including;

at least one filter circuit stage which is not connected to phase-modifying resistive means; and

second combining means for combining an output from the at least one filter circuit stage with a second feedback signal derived from the digital output,

said filter means producing a signal for input to the quantizing means;

wherein the at least one filter circuit stage is a first filter circuit stage of the filter means, and wherein the filter means further comprises a second filter circuit stage following the first filter circuit stage, the second filter circuit stage being followed by a buffer, the output from the at least one filter circuit stage of the filter means being combined with the signal derived from the digital output by said second combining means at the output of the buffer following the second filter circuit stage.

5. An analog-to-digital converter having an input for receiving analog signals, the converter comprising:

quantizing means for producing a digital output of the converter;

first combining means for combining the analog input with a first feedback signal derived from the digital output and producing a first combined signal; and

filter means for filtering the first combined signal, the filter means including;

at least two filter circuit stages each comprising a parallel resonant circuit which is not connected to a respective phase-modifying series resistive means; and

second combining means for combining an output from at least one of the filter circuit stages with a second feedback signal derived from the digital output,

said filter means producing a signal for input to the quantizing means;

wherein the quantizing means includes a comparator.

6. An analog-to-digital converter as claimed in claim 5, wherein the comparator is a.c. coupled to the filter means.

7. An analog-to-digital converter having an input for receiving analog signals, the converter comprising:

quantizing means for producing a digital output of the converter;

first combining means for combining the analog input with a first feedback signal derived from the digital output and producing a first combined signal; and

filter means for filtering the first combined signal, the filter means including;

at least one filter circuit stage which is not connected to phase-modifying resistive means; and

second combining means for combining an output from the at least one filter circuit stage with a second feedback signal derived from the digital output,

said filter means producing a signal for input to the quantizing means;

wherein the quantizing means includes a comparator;

wherein the converter further comprises a buffer having a pair of differential inputs, and d.c. feedback means for providing a third feedback signal derived from the digital output, wherein the at least one filter circuit stage is connected to one of said buffer inputs, the d.c. feedback means being connected to another of the buffer inputs.

8. An analog-to-digital converter as claimed in claim 7, wherein the d.c. feedback means includes a digital-to-analog converter connected to an output of the quantizing means followed by an integrator connected to the buffer input.

9. An analog-to-digital converter having an input for analog signals, the converter comprising:

quantizing means for producing a digital output of the converter;

first combining means for combining the analog input with a feedback signal derived from the digital output with the analog input and producing a first combined signal; and

filter means for filtering the first combined signal, the filter means including;

at least one filter circuit stage which is not connected to phase modifying resistive means,

at least one buffer, having a pair of differential inputs, and

resistive means,

wherein the at least one filter circuit is connected between ground and one input of the pair of differential inputs, and the resistive means is connected to another input of the pair of differential inputs.

10. An analog-to-digital converter as claimed in claim 9, wherein the at least one filter circuit stage of the filter means is followed by the buffer having a pair of differential inputs.

11. An analog-to-digital converter as claimed in claim 9, wherein the quantizing means includes a comparator.

12. An analog-to-digital converter as claimed in claim 11, wherein the comparator is a.c. coupled to the filter means.

13. An analog-to-digital converter as claimed in claim 11, wherein the resistive means comprises d.c. feedback means for providing a second feedback signal derived from the output of the converter.

14. An analog-to-digital converter as claimed in claim 13, wherein the d.c. feedback means includes a digital-to-analog converter connected to an output of the quantizing means followed by an integrator connected to said other differential input of the buffer.