Low FPN high gain capacitive transimpedance amplifier for use with capacitive sensors

• US 6,339,363 B1
• Filed: 12/04/2000
• Issued: 01/15/2002
• Est. Priority Date: 12/04/2000
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Pixel Devices International, Inc. (Agilent Technologies, Inc.)
• Inventors: Fowler, Boyd
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Choe, Henry
• Application Number:
  US09/729,756
• Time in Patent Office: 407 Days
• Field of Search: 330/9, 330/51, 330/86, 330/110, 330/308, 250/214.A, 327/337, 327/344, 327/345, 327/554
• US Class Current: 330/308
• CPC Class Codes: H03F 3/087 with IC amplifier blocks H03F3/085 takes precedence
• CPC Class Codes: H04N 25/60 Noise processing, e.g. detecting, correcting, reducing or removing noise
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion
• CPC Class Codes: H04N 25/78 Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters

Abstract

An amplifier for measuring the charge stored on a source capacitor having a capacitance C_pd. The amplifier includes an opamp having a signal input, reference input and output; the first terminal of the source capacitor is connected to the signal input. The amplifier includes a reset switch for shorting the signal input and the output of the opamp, and a capacitive network. The capacitive network connects the signal input and the output of the opamp, and provides a capacitance of C_T between the signal input and the output of the opamp wherein C_T<C_pd. The capacitive network is constructed from a plurality of component capacitors. Preferably each component capacitor has a capacitance greater than or equal to C_pd. In one embodiment of the invention, the capacitive network includes first, second, and third component capacitors, each capacitor having first and second terminals. The first terminal of the first capacitor is connected to the output of the opamp; the second terminal of the first capacitor, the first terminal of the second capacitor, and the first terminal of the third capacitor are connected together at a first common node, the second terminal of the third capacitor is connected to the signal input of the opamp, and the second terminal of the second capacitor is connected to the second terminal of the parasitic capacitor. The capacitive network also includes a first network switch for connecting the first common node to the output of the opamp.

Claims

1. An amplifier for measuring the charge on a source capacitor having first and second terminals and a capacitance of C_pd, said amplifier comprising:

an opamp having a signal input, reference input and output, said first terminal of said source capacitor being connected to said signal input;

a reset switch for shorting said signal input and said output of said opamp; and

a capacitive network connecting said signal input and said output of said opamp, said capacitive network providing a capacitance of C_T between said signal input and said output of said opamp wherein C_T<

C_pd and wherein said capacitive network is constructed from a plurality of component capacitors, each capacitor of said capacitive network having a capacitance value greater than or equal to C_T.

2. The amplifier of claim 1 wherein each component capacitor has a capacitance greater than or equal to C_pd.

3. An amplifier for measuring the charge on a source capacitor having first and second terminals and a capacitance of C_pd, said amplifier comprising:

an opamp having a signal input, reference input and output, said first terminal of said source capacitor being connected to said signal input;

a reset switch for shorting said signal input and said output of said opamp; and

a capacitive network connecting said signal input and said output of said opamp, said capacitive network providing a capacitance of C_T between said signal input and said output of said opamp wherein C_T<

C_pd and wherein said capacitive network is constructed from a plurality of component capacitors,

wherein said capacitive network comprises first, second, and third component capacitors, each capacitor having first and second terminals, said first terminal of said first capacitor being connected to said output of said opamp;

said second terminal of said first capacitor, said first terminal of said second capacitor, and said first terminal of said third capacitor being connected together at a first common node, said second terminal of said third capacitor being connected to said signal input of said opamp, and said second terminal of said second capacitor being connected to said second terminal of said source capacitor, said capacitive network further comprising a first network switch for connecting said first common node to said output of said opamp.

4. The amplifier of claim 3 wherein said first capacitor comprises a network constructed from fourth, fifth, and sixth component capacitors, said fourth, fifth, and sixth component capacitors being connected such that said fourth, fifth, and sixth capacitors are connected together at a common node, said network further comprising a second network switch for connecting said common node to said output of said opamp.