Integrating/SAR ADC and method with low integrator swing and low complexity

• US 7,511,648 B2
• Filed: 02/29/2008
• Issued: 03/31/2009
• Est. Priority Date: 04/23/2007
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Doorenbos, Jerry L., Trifonov, Dimitar T.
• Primary Examiner(s): Nguyen; Linh V
• Application Number:
  US12/072,968
• Publication Number:
  US 20080258959A1
• Time in Patent Office: 396 Days
• Field of Search: 341/118, 341/120, 341/143, 341/155, 341/156, 341/161, 341/172
• US Class Current: 341/143
• CPC Class Codes: H03M 1/145 the steps being performed sequentially in series-connected stages H03M1/141, H03M1/143, H03M1/16 take precedence
• CPC Class Codes: H03M 1/46 with digital/analogue converter for supplying reference values to converter
• CPC Class Codes: H03M 3/46 using a combination of at least one delta-sigma modulator in series with at least one analogue/digital converter of a different type

Abstract

A reconfigurable circuit (10) includes an integrator (30) having switches (SW1-6) for selectively coupling input capacitors (C0,1,2,3,6,7) and integrating capacitors (C4,5) to terminals of the integrator (30) for operation of a hybrid delta-sigma/SAR ADC (400) so as to create a reference voltage value (Vref) equal to the sum of a first voltage (ΔVbe) and a second voltage (Vbe). A first integration is performed to reduce the integrator output voltage swing. A residue (Vresidue) of the integrator is multiplied by 2. Then the second voltage (Vbe) is integrated in a first direction if a comparator (22) coupled to the integrator changes state or in an opposite direction if the comparator does not change state. The first voltage (ΔVbe) is integrated in a direction that causes the integrator output voltage (Vout) to equal either 2×Vresidue−Vref or 2×Vresidue+Vref.

Claims

1. Reconfigurable circuitry in a hybrid delta-sigma/SAR ADC (analog-to-digital) circuit for converting an input voltage to a digital result, the reconfigurable circuitry comprising:

an integrator including;

an amplifier;

a plurality of input capacitors and first and second integrating capacitors; and

a plurality of switches for selectively coupling the plurality of input capacitors and the first and second integrating capacitors between various terminals of the amplifier and input terminals of the integrator to effectuate operation of the hybrid delta-sigma/SAR ADC in delta-sigma ADC and SAR ADC modes thereof;

a comparator having an input coupled to an output of the integrator, an output of the comparator being coupled to MSB/LSB combination logic of the hybrid delta-sigma/SAR ADC circuit;

digital control circuitry coupled to control electrodes of the plurality of switches for controlling the plurality of switches by performing a plurality of cycles of SAR ADC operation for generating each of one or a plurality of SAR bits; and

the digital control circuitry creating an entire reference voltage value equal to the sum of a first voltage and a second voltage, a first cycle including multiplying a residue voltage of the integrator by 2, a second cycle integrating the second voltage in a first direction by means of the integrator if the comparator changes state or in a second direction opposite to the first direction if the comparator does not change state, and a third cycle integrating the first voltage in a direction that causes the integrator output voltage to equal either 2×

Vresidue−

Vref or 2×

Vresidue+Vref, wherein Vresidue is a residue voltage which is an output voltage of the integrator at the end of a preceding cycle and Vref is equal to the entire reference voltage value.

2. The reconfigurable circuitry of claim 1 wherein the first voltage is the input voltage.

3. The reconfigurable circuitry of claim 2 wherein the first voltage is a PTAT (proportional to absolute temperature) voltage and the second voltage is inversely proportional to temperature.

4. The reconfigurable circuitry of claim 2 wherein the digital control circuitry performs a fourth cycle before the first, second and third cycles, the fourth cycle including integrating a value of the input voltage in a second direction by means of the integrator so as to substantially reduce a voltage swing of the output of the integrator.

5. The reconfigurable circuitry of claim 1 wherein the second cycle is performed after the first cycle and the third cycle is performed after the second cycle.

6. The reconfigurable circuitry of claim 1 wherein the third cycle is performed before the second cycle.

7. The reconfigurable circuitry of claim 1 wherein the amplifier is a differential operational amplifier.

8. The reconfigurable circuitry of claim 1 wherein each of the plurality of switches includes a single pole, double throw switch circuit.

9. The reconfigurable circuitry of claim 8 wherein each of the plurality of switches is controlled by the digital control circuitry.

10. The reconfigurable circuitry of claim 4 wherein each of the plurality of switches is controlled by the digital control circuitry and wherein the digital control circuitry executes an algorithm represented by

Cycle 1:

If (Vresidue >

     0) then  

 

If (Vbe >

Δ

Vbe) then  

 

 

 

Vout1 = (Vresidue −

Δ

Vbe)  

 

Else  

 

 

 

Vout1 = (Vresidue −

Vbe)  

 

End If  

 

State0 = 1 Else  

 

If (Vbe >

Δ

Vbe) then  

 

 

 

Vout1 = (Vresidue + Δ

Vbe)  

 

Else  

 

 

 

Vout1 = (Vresidue + Vbe)  

 

End If  

 

State0 = 0 End If

Cycle 2;

If (Vresidue >

     0) then  

 

 

 

State1= 1 Else  

 

 

 

State1 = 0 End If Vout2 = 2*(Vresidue)

Cycle 3;

If (State0 =

     1) then  

 

If (Vbe >

Δ

Vbe) then  

 

 

 

If (State1=

     1) then  

 

 

 

 

 

Vout3 = (Vresidue −

Vbe)  

 

 

 

Else  

 

 

 

 

 

Vout3 = (Vresidue + Δ

Vbe)  

 

 

 

End If  

 

Else  

 

 

 

If (State1=

     1) then  

 

 

 

 

 

Vout3 = (Vresidue −

Δ

Vbe)  

 

 

 

Else  

 

 

 

 

 

Vout3 = (Vresidue + Vbe)  

 

 

 

End If  

 

End If Else  

 

If (Vbe >

Δ

Vbe) then  

 

 

 

If (State1=

     1) then  

 

 

 

 

 

Vout3 = (Vresidue −

Δ

Vbe)  

 

 

 

Else  

 

 

 

 

 

Vout3 = (Vresidue + Vbe)  

 

 

 

End If  

 

Else  

 

 

 

If (State1=

     1) then  

 

 

 

 

 

Vout3 = (Vresidue −

Vbe)  

 

 

 

Else  

 

 

 

 

 

Vout3 = (Vresidue + Δ

Vbe)  

 

 

 

End If  

 

End If End If

Cycle 4;

If (State0 =

     1) then  

 

If (Vbe >

Δ

Vbe) then  

 

 

 

If (State1=

     1) then  

 

 

 

 

 

Vout4 = (Vresidue + Δ

Vbe)  

 

 

 

Else  

 

 

 

 

 

Vout4 = (Vresidue −

Vbe)  

 

 

 

End If  

 

Else  

 

 

 

If (State1=

     1) then  

 

 

 

 

 

Vout4 = (Vresidue + Vbe)  

 

 

 

Else  

 

 

 

 

 

Vout4 = (Vresidue −

Δ

Vbe)  

 

 

 

End If  

 

End If Else  

 

If (Vbe >

Δ

Vbe) then  

 

 

 

If (State1=

     1) then  

 

 

 

 

 

Vout4 = (Vresidue + Vbe)  

 

 

 

Else  

 

 

 

 

 

Vout4 = (Vresidue −

Δ

Vbe)  

 

 

 

End If  

 

Else  

 

 

 

If (State1=

     1) then  

 

 

 

 

 

Vout4 = (Vresidue + Δ

Vbe)  

 

 

 

Else  

 

 

 

 

 

Vout4 = (Vresidue −

Vbe)  

 

 

 

End If  

 

End If End If,

wherein Vresidue is a residue voltage which is an output voltage of the integrator at the end of a preceding cycle, Δ

Vbe is the first voltage, Vout1, Vout2, Vout3, and Vout4 are the values of the output of the integrator at ends of the fourth, first, second, and third cycles, respectively, Vbe is the second voltage, and Vref is the entire reference voltage value.

11. The reconfigurable circuitry of claim 1 wherein the integrator includes first, second, third, fourth, fifth, and sixth input capacitors, the first and second integrating capacitors, and first, second, third, fourth, fifth and sixth switches, wherein the first input capacitor is connected between a first conductor and a pole of the first switch, the second input capacitor is connected between a second conductor and a pole of the second switch, the third input capacitor is connected between the second conductor and a pole of the fourth switch, the fourth input capacitor is connected between the first conductor and a pole of the third switch, the first conductor is coupled to a pole of the fifth switch and a non-inverting input of the amplifier, the second conductor is connected to a pole of the sixth switch and an inverting input of the amplifier, the first integrating capacitor is connected between a first terminal of the fifth switch and a third conductor, the second integrating capacitor is connected between a first terminal of the sixth switch and a fourth conductor, the third conductor is connected to a second terminal of the fifth switch, an inverting output of the amplifier, an inverting input of the comparator, and a first terminal of the fourth switch, the fourth conductor is connected to a second terminal of the sixth switch, a non-inverting output of the amplifier, a non-inverting input of the comparator, and a first terminal of the third switch, a first terminal of the first switch is connected to a first input conductor, a second terminal of the first switch is connected to a supply voltage, a first terminal of the second switch is connected to a second input conductor, a second terminal of the second switch is connected to the supply voltage, the fifth input capacitor is connected between the second conductor and the second input conductor, the sixth input capacitor is connected between the first conductor and the first input conductor, the first input conductor is connected to a second terminal of the third switch, and the second input conductor is connected to a second terminal of the fourth switch.

12. The reconfigurable circuitry of claim 2 wherein the input voltage is produced by an input circuit including first and second transistors and first and second variable current sources so as to cause the input voltage to represent a temperature of the first and second transistors, the first transistor having an emitter connected to a supply voltage and a base and collector connected by a first input conductor to the first variable current source, the second transistor having an emitter connected to the supply voltage and a base and collector connected by a second input conductor to the second variable current source, the input voltage being applied between the first and second input conductors.

13. The reconfigurable circuitry of claim 12 wherein the digital circuitry controls values of currents produced by the first and second variable current sources, respectively, so as to establish a desired amplitude of the second voltage and a desired amplitude and polarity of the input voltage.

14. The reconfigurable circuitry of claim 10 wherein the algorithm limits an amplitude of the output voltage produced by the integrator to thereby allow accurate operation of the reconfigurable circuitry with a low power supply voltage.

15. The reconfigurable circuitry of claim 13 wherein the reconfigurable circuitry and the hybrid delta-sigma/SAR ADC are configured to provide a digital temperature sensor in a single integrated circuit chip.

19. The method of claim 15 including producing the input voltage by controlling amounts of current through first and second diode-connected transistors so as to produce the input voltage as a difference between base-emitter junction voltages of the first and second diode-connected transistors representing a temperature of the first and second diode-connected transistors.

20. The method of claim 19 including controlling values of the currents through the first and second diode-connected transistors so as to establish a desired amplitude of the second voltage and a desired amplitude and polarity of the input voltage.

16. A method of operating reconfigurable circuitry in a hybrid delta-sigma/SAR ADC (analog-to-digital converter),

the reconfigurable circuitry including an integrator including an amplifier, a plurality of input capacitors, first and second integrating capacitors, a plurality of switches for selectively coupling the plurality of input capacitors and the first and second integrating capacitors to various terminals of the amplifier and input terminals of the integrator to effectuate operation of the hybrid delta-sigma/SAR ADC in delta-sigma ADC and SAR ADC modes thereof, and a comparator coupled to an output voltage of the integrator, the method comprising:

controlling the plurality of switches by performing a plurality of cycles of SAR operation of the hybrid delta-sigma/SAR ADC for generating each of a plurality of SAR bits, the controlling in effect creating an entire reference voltage value equal to the sum of a first voltage and a second voltage;

performing a first cycle by multiplying a residue voltage of the integrator by 2;

performing a second cycle by integrating the second voltage in a first direction by means of the integrator if the comparator changes state or in a second direction opposite to the first direction if the comparator does not change state; and

performing a third cycle by integrating the first voltage in a direction that causes the output voltage of the integrator to equal either 2×

Vresidue−

Vref or 2×

Vresidue+Vref, wherein Vresidue is a residue voltage which is an output voltage of the integrator at the end of a preceding cycle and Vref is equal to the entire reference voltage value.

17. The method of claim 16 wherein the first voltage is an input voltage of the hybrid delta-sigma/SAR ADC.

18. The method of claim 17 including performing a fourth cycle before the first, second and third cycles, the fourth cycle including integrating a value of the input voltage in a second direction by means of the integrator so as to substantially reduce a voltage swing of the output voltage of the integrator.

21. Reconfigurable circuitry in a hybrid delta-sigma/SAR ADC (analog-to-digital converter), comprising:

integrating means including an amplifier, a plurality of input capacitors, first and second integrating capacitors, a plurality of switches for selectively coupling the plurality of input capacitors and the first and second integrating capacitors to various terminals of the amplifier and input terminals of the integrator to effectuate operation of the hybrid delta-sigma/SAR ADC in delta-sigma ADC and SAR ADC modes thereof, and a comparator coupled to an output voltage of the integrator;

means for controlling the plurality of switches by performing a plurality of cycles of SAR operation of the hybrid delta-sigma/SAR ADC for generating each of a plurality of SAR bits, the controlling in effect creating an entire reference voltage value equal to the sum of a first voltage and a second voltage;

means for performing a first cycle by multiplying a residue voltage of the integrator by 2;

means for performing a second cycle by integrating the second voltage in a first direction by means of the integrator if the comparator changes state or in a second direction opposite to the first direction if the comparator does not change state; and

means for performing a third cycle by integrating the input voltage in a direction that causes the output voltage of the integrator to equal either 2×

Vresidue−

Vref or 2×

Vresidue+Vref, wherein Vresidue is a residue voltage which is an output voltage of the integrator at the end of a preceding cycle and Vref is equal to the entire reference voltage value.