Device for clamping multiple signals

• US 6,492,921 B1
• Filed: 05/29/2001
• Issued: 12/10/2002
• Est. Priority Date: 03/24/1999
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Kageyama, Atsuhisa, Kunitani, Hisao
• Primary Examiner(s): Williams, Howard L.
• Application Number:
  US09/856,874
• Time in Patent Office: 560 Days
• Field of Search: 341/118, 341/155
• US Class Current: 341/118
• CPC Class Codes: H03M 1/1225 using time-division multiplexing
• CPC Class Codes: H03M 1/1295 Clamping, i.e. adjusting the DC level of the input signal to a predetermined value
• CPC Class Codes: H04N 5/18 by means of "clamp" circuit operated by switching circuit
• CPC Class Codes: H04N 5/185 for the black level

Abstract

A large number of analog signals (Aa, Ba . . . Na) are time-division-multiplexed by an analog switch (12) into a single analog signal (c). The multiplexed analog signal (c) is converted by an A/D conversion circuit (8) into a digital signal (d). The digital signal (d) is separated by a signal separation circuit (14) into a large number of digital signals (e) respectively corresponding to the analog signals (Aa, Ba . . . Na). Each digital signal (e) is compared by a comparison circuit (9) with a digital reference value (f) having a predetermined value. A current source control circuit (10) generates a digital control signal (g) according to the amount of shift in the digital signal (e) with respect to the digital reference value (f), and the current source (11) is controlled by the control signal (g). Therefore, the clamp level of an analog signal is adjusted to a predetermined level with a high precision, thereby effectively suppressing the level shift thereof.

Claims

1. A device for clamping multiple signals, comprising:

input means to which a plurality of analog signals are input and which cuts off direct-current components of the plurality of analog signals by a plurality of capacitors;

time division multiplexing means for time-division-multiplexing the plurality of analog signals, whose direct-current components have been cut off by the plurality of capacitors, by using an analog switch;

switching control means for controlling the analog switch;

one A-D conversion means for converting an analog signal, which has been obtained through time division multiplexing by the time division multiplexing means, into a digital signal;

signal separation means for separating the digital signal, which has been obtained through conversion by the A-D conversion means, so as to respectively correspond to the plurality of analog signals input to the input means;

comparison means for comparing a plurality of digital signals, which have been obtained through separation by the signal separation means, respectively with a plurality of corresponding digital reference values each having a predetermined value to output a plurality of digital shift amount signals which are amounts of shift respectively in the plurality of digital signals, which have been obtained through separation by the signal separation means, with respect to the corresponding digital reference values;

a plurality of current sources which are provided after the input means, the number of the plurality of current sources corresponds to the number of the plurality of analog signals input to the input means and respectively adjust clamp levels thereof; and

control means for controlling the plurality of current sources,

wherein the plurality of current sources respectively include a plurality of transistors having different output levels, and

wherein the number of the digital shift amount signals corresponds to the number of the plurality of current sources, and the control means controls the plurality of transistors of the plurality of current sources, based respectively on the digital shift amount signals from the comparison means.

2. The device for clamping multiple signals of claim 1, wherein MOS transistors, analog transistors or diodes are used as the plurality of transistors having different output levels included in the current source.