Signal clipping circuit for switched capacitor sigma delta analog to digital converters

• US 6,424,280 B2
• Filed: 01/12/2001
• Issued: 07/23/2002
• Est. Priority Date: 01/21/2000
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sadkowski, Roberto
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): NGUYEN, KHAI M
• Application Number:
  US09/760,286
• Publication Number:
  US 20010050626A1
• Time in Patent Office: 557 Days
• Field of Search: 341/135, 341/136, 341/139, 341/141, 341/143, 341/155, 327/321, 327/327, 327/328
• US Class Current: 341/143
• CPC Class Codes: H03M 3/48 characterised by the type of range control, e.g. limiting
• CPC Class Codes: H03M 3/492 in feed forward mode, i.e. by determining the range to be selected directly from the input signal

Abstract

A mixed signal CODEC including an improved sigma-delta ADC (20) which limits input signals into a switched capacitor configuration and avoids adding circuit overhead in the signal path is disclosed herein. Additionally, it avoids overshoot and settling problems. This sigma-delta analog-to-digital converter (20), having an input signal and an output signal, includes a switch (sw₁), a clipping circuit (21), and a known sigma-delta ADC (34). It solves the clipping signal problem by limiting the signal right at the input of the sigma-delta ADC (34). The clipping circuit (21) couples to the switch (sw₁) and the sigma-delta ADC (34) for switching the voltage applied to the sigma-delta ADC between the input signal (v_in) and at least one threshold voltage (V_n and V_p).

Claims

1. A sigma-delta analog-to-digital converter, having an input signal and an output signal comprising:

a first switch;

a clipping circuit coupled to the first switch for switching between the input signal and at least one threshold voltage, the clipping circuit comprises a first branch for clipping the output signal at an upper boundary, and a second branch for clipping the output signal at a lower boundary, the first branch comprises,

a comparator having an output, a first input coupled to receive a first threshold voltage and a second input coupled to receive the input signal, and

a second switch coupled to the output of the comparator, the output voltage of the comparator couples to the second switch to open and close the second switch; and

a sigma-delta analog-to-digital converter having an input coupled to the first switch.

2. The device of claim 1 wherein the first input of the comparator is a negative input and the second input of the comparator is a positive input.

3. A sigma-delta analog-to-digital converter, having an input signal and an output signal comprising:

a first switch;

a clipping circuit coupled to the first switch for switching between the input signal and at least one threshold voltage, the clipping circuit comprises a first branch for clipping the output signal at an upper boundary, and a second branch for clipping the output signal at a lower boundary, the second branch comprises,

a comparator having an output, a first input coupled to receive a first threshold voltage and a second input coupled to receive the input signal, and

a second switch coupled to the output of the comparator, the output voltage of the comparator couples to the second switch to open and close the second switch; and

a sigma-delta analog-to-digital converter having an input coupled to the first switch.

4. The device of claim 3 wherein the first input of the comparator is a negative input and the second input of the comparator is a positive input.