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STMICROELECTRONICS : Patent Issued for Analog Signal Soft Switching Control with Precise Current Steering Generator

07/24/2014 | 03:36am US/Eastern
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By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Chen, Min (Shenzhen, CN); Liu, Wen (Nanshan, CN); Li, HongXia (Shenzhen, CN); Dai, XiaoWu (Shenzhen, CN), filed on December 3, 2012, was published online on July 15, 2014.

The patent's assignee for patent number 8779801 is STMicroelectronics (Shenzhen) R&D Co. Ltd. (Shenzhen, CN).

News editors obtained the following quote from the background information supplied by the inventors: "A classical implementation of switching between two signals V1 and V2 could be a direct switching with a logical control as shown in circuit 100 of FIG. 1. Two CMOS switches S1 and S2 are used and they are controlled by a reversed logical control signal (CTRL and inverted CTRL through inverter 102). Either signal V1 or V2 is passed through operational amplifier 104 to provide the VOUT output signal. If the two signals have different signal voltages, there will be a jump or step at the output point 106. In some applications, this jump or step of the output signal could create a problem. For example, in an audio application, if the output signal goes to a speaker, the jump will create an undesirable pop noise at the speaker. In this case, a smooth transition between the two input signals is obviously preferred.

"A traditional digital solution 200 for a smooth transition between switched input signals uses resistor networks 212 and 214, as well as corresponding switching networks 216 and 218 to divide a big step into small ones as shown in FIG. 2. Circuit 200 includes an input for receiving a first input signal V1, and a second input for receiving a second input signal V2. Circuit 200 also includes an output operational amplifier or buffer 204, soft-switching clock generator 206, a switch counter 208, and a logic controller 210. Circuit 200 also typically includes a final post processing low pass filter 220. By increasing the number of small steps and the soft-switching time, the pop noise is reduced. In the solution shown in FIG. 2, the resistors and parasitic components will deteriorate performance due to increased noise and Total Harmonic Distortion (THD). For some configurations of step numbers and soft-switching times, undesired audio tones are generated. A low pass filter is needed to remove high frequency digital spikes associated with circuit 200. The digital circuit 200 shown in FIG. 2 presents difficult trade-offs between pop noise and other performance considerations.

"What is desired, therefore, is a simple analog switching circuit for providing a smooth transition between two input signals, and without the need for any post-processing or filtering, or without the use of complex digital circuitry."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "According to the present invention, a signal switching circuit and method based on analog current transition is presented, which can be utilized in many applications, such as audio applications, to switch from one signal to another with a smooth transition.

"A switching circuit comprises a first input stage having an input for receiving a first input signal, an output, and a power terminal for receiving an increasing analog current, a second input stage having an input for receiving a second input signal, an output, and a power terminal for receiving a decreasing analog current, and an output node coupled to the outputs of the first input stage and the second input stage for providing a switched output signal. An output stage is interposed between the first and second input stages and the output node. The first and second input stages each comprise an operational amplifier.

"A corresponding switching method comprises applying a first input signal to a first input stage, applying an increasing analog current to a power terminal of the first input stage, applying a second input signal to a second input stage, applying a decreasing analog current to a power terminal of the second input stage, and combining output signals from the first input stage and the second input stage to provide a switched output signal. The switched output signal can be buffered, and the first and second input stages can comprise operational amplifiers.

"According to an embodiment of the present invention, the switching circuit can comprise a current generator for receiving a clock signal and for generating a charge current and a discharge current, a voltage generator for receiving the charge and discharge current and for providing a control voltage, a voltage-to-current generator for receiving the control voltage and for providing a first analog current and a second analog current, and an amplifier stage for combining the first and second analog currents and for providing a switched output signal.

"The current generator comprises first and second integrators having inputs switched by the clock signal, two additional voltage-to-current generators having outputs switched by the clock signal, and first and second current mirrors having inputs switched by the clock signal.

"The voltage generator comprises first and second current mirrors, receives two additional clock signals, and comprises a load capacitor.

"The voltage-to-current generator comprises a differential amplifier for receiving the control voltage, a reference voltage, and for providing the first and second analog currents, as well as first and second current mirrors.

"The amplifier stage comprises first and second input stages, and an output stage coupled to outputs of the first and second input stages. Each of the stages can comprise an operational amplifier or buffer.

"According to the present invention, the first analog current comprises an analog current increasing from a first value to a second value, and the second analog current comprises an analog current decreasing from the second value to the first value."

For additional information on this patent, see: Chen, Min; Liu, Wen; Li, HongXia; Dai, XiaoWu. Analog Signal Soft Switching Control with Precise Current Steering Generator. U.S. Patent Number 8779801, filed December 3, 2012, and published online on July 15, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8779801.PN.&OS=PN/8779801RS=PN/8779801

Keywords for this news article include: STMicroelectronics.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC

(c) 2014 NewsRx LLC

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