Patent number 8610469 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Low-distortion programmable-gain amplifiers have many applications. For example they are useful in processing analog audio signals where it is important to preserve the integrity of the signals. One prior art implementation of a low-distortion programmable-gain amplifier is shown in FIG. 1. An input signal, which may be AC or DC, is applied to the input V.sub.IN. The output signal appears at the output V.sub.OUT. In this embodiment the high-gain operational amplifier A.sub.1 is configured as a non-inverting amplifier. This configuration is preferred for low-noise applications over the inverting configuration since the feedback network can be made low impedance to minimize its thermal noise contribution without compromising the amplifier input impedance, which may be set independently via resistor R.sub.IN. The feedback network around operational amplifier A.sub.1 is tapped at any one of a plurality of points by selectively controlling the corresponding electronic switch elements S.sub.1 through S.sub.N. These switch elements are typically each constructed of complementary metal-oxide semiconductor (CMOS) devices. Control signals (C.sub.1 through C.sub.N) select the desired gain by turning on the associated switch. Such an approach has the benefit that the variations in ON-resistance of electronic switches S.sub.1 through S.sub.N due to changes in input voltage do not affect the linearity of the output signal since no signal current flows through these switches. This minimizes distortion, so long as one and only one of electronic switches S.sub.1 through S.sub.N is turned on at any one moment in time.
"However, the ON-resistance of each of these switches does contribute thermal noise to the total input noise of the amplifier. One way to decrease the ON-resistance of CMOS electronic switches (and thus to reduce the amplifier's input noise) is to increase the physical width of the CMOS devices which make up the switches. In an integrated circuit, however, an increase in the width of a switch results in an increased die area. Since the approach illustrated in FIG. 1 requires one switch for each desired gain setting, the necessary area taken by the switches in an integrated circuit can be a significant issue.
"Another aspect of CMOS electronic switches is that modern CMOS processes often do not allow large voltages to be applied between the gate and channel (source and drain) of the switches, even for so-called 'high-voltage' CMOS processes. This can limit the analog voltages which may be switched by CMOS electronic switches, thus restricting the maximum analog voltages, Vin, which can be applied at input of the switch.
"Accordingly, it is desirable to provide a dynamic switch driver for a low-distortion programmable-gain amplifier that overcomes or at least substantially reduces the foregoing disadvantages."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "In accordance with one aspect of the invention, a switching circuit for switching a time varying input signal is provided. The switching circuit comprises: at least one switch including a N-channel MOSFET and a P-channel MOSFET, each having a gate configured to receive a drive signal to change the ON/OFF state of the switch; and a drive circuit configured and arranged so as to selectively apply a pair of drive signals to change the ON/OFF state of the switch, the drive circuit being configured and arranged to generate the drive signals as a function of (a) a pair DC signal components sufficient to change the ON/OFF state of the switch and (b) a pair of varying signal components as at least a partial replica of the signal present on the source terminal of each MOSFET so that when applied with the DC signals to the gates of the n-channel MOSFET and p-channel MOSFET respectively, the drive signals will be at the appropriate level to maintain the ON/OFF state of the switch and keep the gate-source voltages of each MOSFET within the gate-source breakdown limit of the MOSFETs.
"In accordance with another aspect of the invention, a method of switching a time varying input signal uses at least one switch including a N-channel MOSFET and a P-channel MOSFET, each having a gate configured to receive a drive signal to change the ON/OFF state of the switch. The method comprises: selectively applying a pair of drive signals to change the ON/OFF state of the switch by generating the drive signals as a function of (a) a pair DC signal components sufficient to change the ON/OFF state of the switch and (b) a pair of varying signal components as at least a partial replica of the signal present on the source terminal of each MOSFET so that when applied with the DC signals to the gates of the n-channel MOSFET and p-channel MOSFET respectively, the drive signals will be at the appropriate level to maintain the ON/OFF state of the switch and keep the gate-source voltages of each MOSFET within the gate-source breakdown limit of the MOSFETs.
"Although reference is made herein to switching 'AC signals', it should be understood that the term 'AC signals' is not intended to be limited to signals that return to ground (with no DC component), but also include any time varying signals whose amplitude varies over time, and can include DC signals of either polarity, and signals whose amplitude can include DC components so as to include both polarities over time."
URL and more information on this patent, see: Hebert,
Keywords for this news article include: THAT Corporation.
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