Abstract: A memory system includes a sense amplifier for detecting content of data memory cells by comparison with a voltage stored in a reference cell. The sense amplifier may comprise a comparator, first and second load circuits, and a low impedance circuit. A first input of the comparator is coupled to the low impedance circuit and a reference voltage node. A second input of the comparator is coupled to a data voltage node. The first load circuit loads a reference cell coupled to the reference voltage node. The second load circuit loads a data cell coupled to the data voltage node.

Abstract: A power up circuit that having reduced power consumption during power saving modes, while maintaining an active flag signal indicating that the power supply voltage is satisfactory. This is achieved by turning off the power up circuit during the power saving mode, and using a status holding circuit to maintain the active flag signal in response to the power down signal. The status holding circuit is responsive to an internal node of the power up circuit for generating the active flag signal when the internal node has reached a predetermined level. The power down signal can be one or both a sleep mode signal and a deep power down signal. The status holding comprises an override circuit for maintaining the active flag signal in the power saving mode, and a restore circuit for rapidly resetting at least the internal node of the power up circuit upon exit of the power saving mode.

Abstract: A memory system includes a sense amplifier for detecting content of data memory cells by comparison with a voltage stored in a reference cell. The sense amplifier may comprise a comparator, first and second load circuits, and a low impedance circuit. A first input of the comparator is coupled to the low impedance circuit and a reference voltage node. A second input of the comparator is coupled to a data voltage node. The first load circuit loads a reference cell coupled to the reference voltage node. The second load circuit loads a data cell coupled to the data voltage node.

Abstract: A high-speed receiver suitable for applications that desire a common-mode voltage range from approximately 0.7V to approximately 0.9V is arranged by coupling first and second differential pair circuit architectures based on first and second current-steering schemes into the same path to generate an output signal. The high-speed receiver includes first and second differential pair circuits. The first differential pair circuit is coupled to a first current-steering path via a first port and a second current-steering path via a second port. The second differential pair circuit is coupled to the first current-steering path via a third port and the second current-steering path via a fourth port. A bridge circuit is interposed between the first and second differential pair circuits. The bridge circuit integrates the first and second current-steering paths in a single-stage of the high-speed receiver assembly.

Abstract: A high-voltage switch circuit includes an enable control circuit, a feedback circuit, a boosting circuit, and a high voltage switch. The enable control circuit precharges an output node to a set voltage in response to an enable signal. The feedback circuit supplies a feedback voltage to an input node in response to a switch control voltage generated from the output node when the output node is precharged. The boosting circuit boosts the feedback voltage and outputs a boosting voltage to the output node, in response to clock signals, thereby increasing the switch control voltage. The high voltage switch is turned on or off in response to the switch control voltage, and is turned on to receive a high voltage and output the received high voltage. The boosting circuit includes an amplification circuit of a cross-coupled type.

Abstract: A semi-dual reference voltage data receiving apparatus includes a first input buffer, a second input buffer, and a phase detector wherein the first input buffer includes a first input receiving unit, a first sense amplifier, and a first current offset controlling unit. The first sense amplifier senses and amplifies the voltage difference between the voltage of a first terminal of a first input transistor and the voltage of a first terminal of a second input transistor. The first current offset controlling unit controls the offset of the current that flows through the second terminal of the second input transistor.

Abstract: A differential comparator is provided. The comparator receiving two differential signals and generating a comparison result represented by an output signal on one of two output terminals respectively on two current paths. The comparator comprises two pairs of latch transistors respectively disposed on the two current paths and two pairs of input transistors respectively disposed on the two current paths, wherein gates of the latch transistors on one of the current paths are commonly coupled to the output terminal between the latch transistors on the other current path, gates of the input transistors on one of the current paths respectively receives an input signal of one of the differential signals and a reference signal of the other differential signal and each of the input transistors is disposed between the output terminal and one of the latch transistors on the current path thereof.

Abstract: Methods and systems are provided for comparing currents. The method includes driving a first current through a first X leg of a first current conveyor circuit and a second current through a second X leg of a second current conveyor circuit. The method further includes draining a third current from a first X terminal of the first current conveyor circuit to produce a first positive transistor current and a first negative transistor current, and draining a fourth current from a second X terminal of the second current conveyor circuit to produce a second positive transistor current and a second negative transistor current. The method further includes summing the first positive transistor current and the second negative transistor current to produce a first current output, the first negative transistor current and the second positive transistor current to produce a second current output, and the first current output and the second current output to produce a summed current output.

Abstract: A sense amplifier includes a reference voltage generator for generating a reference output voltage and a core output voltage generator for generating a core output voltage. The core output voltage generator includes a core front-end stage and a core back-end stage or includes a plurality of amplifier transistors each conducting a portion of a core current through a current conducting device such as core cell. The sizes and/or connections of transistors of such components result in high voltage swing and thus high sensitivity of the sense amplifier.

Abstract: A differential current-sensing amplifier includes two inverters, two resistors, a NOR gate, and five switches. The first inverter has a first output; the second inverter has a second output. The first resistor is connected between the first inverter and ground; the second resistor is connected between the second inverter and ground. A current to be sensed is input between the first resistor and the first inverter; a reference current is input between the second resistor and the second inverter. The first switch is connected between the first output and ground, the second switch is connected between the second output and ground, and the third switch is connected between the first and the second inverters and power. The first and the second switches are turned off, and the third switch is turned on, to compare the current to be sensed in relation to the reference current.

Abstract: Sensing circuitry and a method of operating such sensing circuitry are provided. The sensing circuitry has voltage change detection circuitry for detecting a change in voltage on at least one input line and for producing at least one output signal indicative of that change during a sensing stage of operation. The voltage change detection circuitry comprises at least one latch transistor having a body region insulated from a substrate. Further, body biasing circuitry is provided which, prior to the sensing stage of operation, causes a voltage to be applied to the body region that is derived from the voltage on one of said at least one input lines. Then, during the sensing stage of operation, the body biasing circuitry causes the voltage of the body region to float. Such an arrangement enables removal of the history effect that can sometime affect such latch transistors, whilst alleviating power consumption and noise issues that can occur in certain known sensing circuits.

Abstract: A voltage comparator having hysteresis includes a comparing section that compares an input voltage with a reference voltage so as to output a high-level or low-level signal; and a reference voltage changing section that changes the reference voltage when a low-level signal is output from the comparing section.

Abstract: Provided is an amplifier circuit having a constant output swing range and a stable delay time, where the amplifier circuit includes a first bias unit, a second bias unit, a comparison unit, and an amplifier unit, and the first bias unit responds to an internal reference signal with a predetermined voltage level and maintains constant the amount of a first current, and the second bias unit receives an external reference signal, responds to a control voltage, and controls the amount of a second current to be the same as the amount of the first current, and the comparison unit compares a voltage level of a first node with a voltage level of a second node, and controls a voltage level of the control voltage according to the comparison result, and the amplifier unit compares a voltage level of an external input signal with a voltage level of the external reference signal, amplifies and outputs a voltage difference between the two compared signals, responds to the control voltage, and controls the amount of a third

Abstract: An offset current independent sense circuit is switchable between a store state and a sense state. In the store state, the sense circuit stores an offset current to a capacitor, and the influence of the offset current is eliminated by a transistor to regenerate the offset current based on a signal provided by the capacitor in the sense state.

Abstract: A differential current-sensing amplifier includes two inverters, two resistors, and three switches. The first inverter has a first output and the second inverter has a second output. The first resistor is connected between the first inverter and ground, and the second resistor is connected between the second inverter and ground. A current to be sensed is input between the first resistor and the first inverter, and a reference current is input between the second resistor and the second inverter. The first switch is connected between the first output and ground, the second switch is connected between the second output and ground, and the third switch is connected between the first and the second inverters and power. The first and the second switches are turned off, and the third switch is turned on, to compare the current to be sensed in relation to the reference current.

Abstract: In accordance with some embodiments, a current-balanced logic circuit includes a first sense amplifier, a second sense amplifier, and a current-source transistor which provides bias current to the first and second sense amplifiers. The first and second sense amplifiers are alternately activated by first and second differential clock signals, and when activated convert data received on differential input lines into logical values for storage in respective storage circuits. The storage circuits may be flip-flops, latches, keeper circuits, or other circuits for storing data.

Abstract: An electrically programmable multiple selectable function integrated circuit module has a plurality of optionally selectable function circuits, which receive and manipulate a plurality of input data signals. The outputs of the plurality of optionally selectable function circuits are either interconnected to each other or connected to a plurality of output connectors to transmit manipulated output data signals to external circuitry. The electrically programmable multiple selectable function integrated circuit module has at least one configuration connector, which may be multiplexed with input control and timing signals, connected to a function configuration circuit to receive electrical configuration signals indicating the activation of a program mode and which of the optionally selectable function circuits are to be elected to manipulate the input data signals.

Abstract: A memory system includes a sense amplifier for detecting content of data memory cells by comparison with a voltage stored in a reference cell. The sense amplifier may comprise a comparator, first and second load circuits, and a low impedance circuit. A first input of the comparator is coupled to the low impedance circuit and a reference voltage node. A second input of the comparator is coupled to a data voltage node. The first load circuit loads a reference cell coupled to the reference voltage node. The second load circuit loads a data cell coupled to the data voltage node.

Abstract: A signal-processing circuit has a first and a second input, which receive a first and a second differential signal, a third input, which receives a common-mode signal, the first and second differential signals having an equal and substantially opposite trend with respect to the common-mode signal, and a first output supplying a first processed signal, equivalent to the first differential signal rectified with respect to the common-mode signal, and satisfying throughout its course a first relation of comparison with the common-mode signal. The processing circuit is provided with first formation means for formation of the first processed signal, which operate on the basis of the first differential signal, and second formation means for formation of the first processed signal, which operate on the basis of the second differential signal; the first and second formation means co-operate in the formation of the first processed signal.

Abstract: A sense amplifier includes a reference voltage generator for generating a reference output voltage and a core output voltage generator for generating a core output voltage. The core output voltage generator includes a core front-end stage and a core back-end stage or includes a plurality of amplifier transistors each conducting a portion of a core current through a current conducting device such as core cell. The sizes and/or connections of transistors of such components result in high voltage swing and thus high sensitivity of the sense amplifier.

Abstract: An offset current independent sense circuit is switchable between a store state and a sense state. In the store state, the sense circuit stores an offset current to a capacitor, and the influence of the offset current is eliminated by a transistor to regenerate the offset current based on a signal provided by the capacitor in the sense state.

Abstract: A voltage-controlled amplifier for a signal processing system includes an input voltage reception end, a first voltage-to-current converter, a reference current generator, a gain adjustment circuit, a first current mirror, and an output circuit. The voltage-controlled amplifier adjusts a gain according to a variable control voltage, so as to transfer an input voltage to an output voltage according to the adjusted gain. When adjusting the gain, the present invention changes only an alternating current part of the input voltage, and can decrease noise, the production cost, and increase integration degree.

Abstract: There is disclosed a semiconductor integrated circuit device capable of eliminating an influence of a power voltage drop generated in a circuit disposed in the semiconductor integrated circuit device to inhibit an operation defect or an operation speed decrease of the circuit. In a semiconductor integrated circuit device 10 including a power wiring 18 connected to a power supply (Vdd) via a power terminal 12, a ground wiring 20 connected to a ground (0 V) via a ground terminal 14, and a plurality of circuits 301 to 30f connected in parallel with one another between the power wiring 18 and the ground wiring 20, a negative power terminal 16 connected to a negative power supply (?Vdd) is disposed, and a current source 22 is disposed as a current generating section between the negative power terminal 16 and a node Gf on a ground wiring 20 side of the f-th circuit 30f disposed in a region most distant from the ground.

Abstract: An amplification apparatus is provided that includes a plurality of gain stages including a first gain stage having first and second transistors and a second gain stage having third and fourth transistors. A plurality of replica stages may also be provided that includes a first replica stage and a second replica stage. Each replica stage may correspond/match one of the plurality of gain stages. An amplifying device may be provided to adjust a body potential of at least the first transistor of the first gain based on an output of the first replica stage and an output of the second replica stage.

Abstract: A redundant battery power supply with combined battery charge indication which incorporates a main cell, conductively coupled to the supply bus which powers the load when activated, and a predictive cell, coupled to the bus by an optional diode which becomes forward biased when the main cell voltage drops below the predictive cell voltage. If the main cell becomes discharged, the predictive cell powers the bus. Each cell is coupled to a voltage comparator which compares the cell output voltage to a common reference voltage. When a cell voltage drops below the reference voltage, the corresponding comparator output goes low. The output of the two comparators are combined by a logical AND gate which controls a flashing light. When both the main cell and predictive cell have voltages greater than the reference voltage, the light flashes, but when either cell (or both) has a voltage less than the reference voltage, the light does not flash.

Abstract: A sense amplifier latch that is operable to interface with high common-mode input voltages with wide ranges for all process variations. The sense amplifier latch comprises a cross-coupled latch having first and second rail signals; a pre-charge device; an equalization device; pass devices for enabling input devices to receive pad and reference inputs. In the present invention, the input devices comprise push-pull impedance dividers are used to preserve the input difference voltage while dramatically lowering the common-mode output voltage. The outputs of the impedance dividers are fed to the cross-coupled latch of the sense amplifier using n-channel pass gates.

Abstract: A semiconductor physical quantity sensing device to perform electrical trimming at low cost by using a CMOS manufacturing process and a small number of terminals. The semiconductor physical quantity sensing device includes a wheatstone bridge circuit, which is a sensor element, an auxiliary memory circuit, which stores provisional trimming data, a main memory circuit, which stores finalized trimming data, an adjusting circuit, which adjusts the output characteristics of the sensor element based on trimming data stored in the auxiliary memory circuit or the main memory circuit, with the elements and circuits being only configured of active elements and passive elements manufactured by way of the CMOS manufacturing process formed on a same semiconductor chip.

Abstract: A clock enable buffer for entry of a self-refresh mode. The clock enable buffer includes a current mirror load connected between a voltage source and first and second nodes, wherein the current mirror load has first and second transistors; a third transistor connected between the first node and a third node, wherein the third transistor is turned on according to a reference voltage; a fourth transistor connected between the second node and the third node, for controlling the current mirror load in response to a clock enable signal; a fifth transistor connected between the third node and a ground, wherein the fifth transistor is turned on according to a self-refresh signal; and a sixth transistor that is turned on according to an inverted self-refresh signal to make the potential of the first node a Low level.

Abstract: A method and apparatus are described for providing an activation signal based on a received radio frequency (RTF) signal. The apparatus includes an RF receiver configured to admit a received RF signal in a given frequency band and a converter configured to convert the admitted RF signal to a proportional signal. The apparatus also includes a low power comparator that has a first and second input and an output. A biasing and offset compensation circuit is configured to bias the proportional signal higher by an offset midrange voltage and bias the second input to an offset compensated voltage based on an offset between the inputs of the comparator. The comparator is configured to receive the biased proportional signal at the first input and produce the activation signal at the output when a voltage difference between the biased proportional signal and the offset compensated voltage exceeds a comparison voltage threshold.

Abstract: A circuit in an integrated circuit having input terminals coupled to a resistor network for selecting one of multiple digital states includes a tri-state circuit, a multiplexer, a comparator and a control circuit. A DAC can be used to generate a set of comparison voltage levels. The circuit detects the power connection and the resistance values of at least two resistors in the resistor network having a third resistor of fixed resistance. The resistance values for the two resistors are selected from a set of resistance values corresponding to the number of digital stages which can be programmed on each terminal. The power connection option doubles the number of digital stages to be programmed on each terminal. Thus, multiple programming states can be assigned to each control pin of an integrated circuit and a large number of programming states can be programmed using a small number of control pins.

Abstract: A multiple matchline sense circuit for detecting a single, more than one, or no match conditions during a search-and-compare operation of a content addressable memory is disclosed. The circuit compares the rising voltage rate of a multiple matchline to the rising voltage rate of a reference multiple matchline in order to generate a multibit result representing one of the three conditions. The circuit generates a self-timed control signal to end the search-and-compare operation, and to set the circuit to a precharge state.

Abstract: An integrated circuit has one or more components that operate with reference to a distributed reference voltage. A reference voltage driver produces a compensated reference voltage, and the compensated reference voltage is distributed to form the distributed reference voltage at the components. Due to factors such as trace resistance and gate leakage, the distributed reference voltage is degraded relative to the compensated reference voltage. The reference voltage driver is responsive to feedback derived from the distributed reference voltage to adjust the compensated reference voltage so that the distributed reference voltage is approximately equal to a nominal reference voltage.

Abstract: A sensor for a switching circuit detects the logical state of the switching circuit by monitoring the current flow through the switching circuit. The current flow is conditioned by one or more current limiters and a voltage regulator, coupled in series with the switching circuit. The sensor also includes a current limit control circuit coupled to each of the current limiters. The sensor is effectively shielded from the effect of parasitic capacitance in the switching device because the current flow through the switching circuit reacts immediately and without regard to the level of parasitic capacitance whenever the switching circuit makes a state change.

Abstract: In one embodiment, a power switch device (33) includes a first MOSFET device 41 and a second MOSFET device (42). A split gate structure (84) including a first gate electrode (48,87) controls the first MOSFET device (41). A second gate electrode (49,92) controls the second MOSFET device (42). A current limit device (38) is coupled to the first gate electrode (48,97) to turn on the first MOSFET device during a current limit mode. A comparator device (36) is coupled to the second gate electrode (49,92) to turn on the second MOSFET device (42) when the power switch device (33) is no longer in current limit mode.

Abstract: The invention is directed to an apparatus and a method for generating a fault detection signal when a differential signal is in a fault condition. The fault condition arises when the data transmission path in a differential signaling device is either open, shorted, or terminated by an abnormal means, and is such that the inputs are within the valid common-mode range and a valid differential signal cannot be obtained. The invention is buffered from the differential signal source, and an intermediate signal is produced in response to the differential signal. Portions of the intermediate signal are compared to a reference signal, and based on the comparisons, fault condition control signals are produced. A fault detection signal is produced when two fault condition control signals indicate the presence of a fault. The fault detection signal is made available for invocation of a failsafe state.

Abstract: A sense amplifier circuit includes a latch circuit to enhance the speed of a sensing operation and to obviate the need for a latch circuit to capture the output value of the sense amplifier circuit. In one embodiment, first and second differential amplifiers provide a differential signal to the latch circuit. The high gain in the latch circuit resolves the differential signal to a logic signal, which is then provided to an output amplifier. In one embodiment, the differential signal is provided to the latch circuit after the differential signal across the input terminals of the first and second differential amplifiers exceeds a predetermined value.

Abstract: The input buffer circuit includes an input stage providing a switching point voltage based on a predetermined switching point set between a first and second reference voltages that maximizes the high and low noise margins of the input buffer. The input buffer circuit further includes an output stage. The output stage is coupled to the input stage. The output stage receives the switching point voltage from the input stage and amplifies the switching point voltage to a full logic level voltage.

Abstract: An integrated circuit has one or more components that operate with reference to a distributed reference voltage. A reference voltage driver produces a compensated reference voltage, and the compensated reference voltage is distributed to form the distributed reference voltage at the components. Due to factors such as trace resistance and gate leakage, the distributed reference voltage is degraded relative to the compensated reference voltage. The reference voltage driver is responsive to feedback derived from the distributed reference voltage to adjust the compensated reference voltage so that the distributed reference voltage is approximately equal to a nominal reference voltage.

Abstract: A method for receiving data by an integrated circuitry chip includes receiving data signals and a first clock signal sent by a sending chip. The data signals are received by data receivers and the clock signal is received by at least one clock receiver of the receiving chip. A reference voltage is derived by reference voltage circuitry for the receiving chip responsive to the first clock signal. Logical states of the received data signals are detected. The detecting includes the data receivers comparing voltage levels of the received data signals to the derived reference voltage.

Abstract: A circuit includes a first pre-amp circuit that provides a first pre-amp current and a second pre-amp circuit that provides a second pre-amp current. A first threshold circuit is configured to generate a first output signal responsive to a difference between a variable current and the first pre-amp current. A second threshold circuit is configured to generate a second output signal responsive to a difference between the variable current and the second pre-amp current. One of the branches of a differential interpolation circuit includes a first transistor that is connected in a current mirror configuration with the first pre-amp circuit. The first transistor has a width/length ratio equal to the product nk, where n<1. A second transistor is connected in a current mirror configuration with the second pre-amp circuit. The second transistor has a width/length ratio equal to the product mk, where m<1 and n+m is about 1.

Abstract: A control clocks generator and method thereof for a high speed sense amplifier generates control clocks by utilizing RC delay and gate delay, in combination with reference sensing delay induced from a reference sense amplifier, and thereby, is tracking well for the high speed sense amplifier with process, temperature and voltage variations.

Abstract: A circuit for controlling a reference node in a sense amplifier switchable between an operating mode and a stand-by mode is provided. The reference node provides a reference voltage in the operating mode. The circuit may include circuitry for bringing the reference node to a starting voltage upon entry into the stand-by mode, circuitry for keeping the reference node at a pre-charging voltage in the stand-by mode, and circuitry for providing a comparison voltage closer to the pre-charging voltage than the starting voltage. Pulling circuitry may also be included for pulling the reference node toward a power supply voltage. Further, a controller may activate the pulling circuitry upon entering the stand-by mode, and disable the pulling circuitry when the voltage at the reference node reaches the comparison voltage.

Abstract: An electronic device such as a processor receives a master clock signal from a system clock generator. The clock signal may be single-ended or differential. The disclosure presents methods and devices for automatically producing a clock signal that follows the master clock signal, regardless of whether the master clock signal is single-ended or differential.

Abstract: A comparator is provided with a pair of transistors which are continuously in ON state, in which a switch unit constructed of a diode pair, for switching a current path in response to a high/low relationship between a voltage level of an input signal and a voltage level of a reference voltage, and a unit for converting a current into a voltage level are provided between emitter terminals of the transistor pair.

Abstract: A sensor for a switching circuit detects the logical state of the switching circuit by monitoring the current flow through the switching circuit. The current flow is conditioned by one or more current limiters and a voltage regulator, coupled in series with the switching circuit. The sensor also includes a current limit control circuit coupled to each of the current limiters. The sensor is effectively shielded from the effect of parasitic capacitance in the switching device because the current flow through the switching circuit reacts immediately and without regard to the level of parasitic capacitance whenever the switching circuit makes a state change.

Abstract: A sense amplifier having a sampling circuit to sample the amplifier input signal; a reference node storing a reference signal corresponding to the input signal; and a timing circuit activating the sampling circuit for a predetermined interval, and admitting the reference signal to the reference node. The sense amplifier also can include a pump capacitor substantially maintaining a value of the reference signal; and a gain circuit coupled with the reference node and disposed to adaptively adjust gain of an output signal produced by the sense amplifier. The sense amplifier can be a single-ended sense amplifier.

Abstract: Clocked full-rail differential logic circuits with sense amplifier and shut-off are activated by a delayed clock and include a sense amplifier circuit that is triggered by a second delayed clock and a shut-off device. The addition of the sense amplifier circuit, and second delayed clock signal allows the sense amplifier circuit to act as the driver and therefore there is no need for increasing the size of the differential logic network to provide a driver function. The addition of the shut-off device provides a full-rail differential logic circuit with shut-off that does not experience the large “dip” experienced by prior art full-rail differential logic circuits and is therefore more power efficient.

Abstract: An anlog boundary scan compliant integrated circuit system carries out a test more reliably and cuts down on power dissipated during normal operation. To perform a test of whether or not an interconnect is connected normally between integrated circuits, multiple logic circuits with mutually different input threshold voltages are provided to detect the logical level of a potential at a terminal, thereby improving the reliability of the test. Potential fixers and power isolators are optionally provided. During normal operation, the power fixers fix the output potentials of the logic circuits, while the power isolators electrically isolate the logic circuits from the ground. As a result, no current flows through the logic circuits or other circuits in succeeding stages while no tests are carried out.

Abstract: A high speed phase detector utilizes an integrated XOR/SUMMER/MUX circuit having a higher bandwidth and lower power than conventional designs. The XOR/SUMMER/MUX circuit combines the functionality of two parallel XOR devices in series with a summer/multiplexer in a manner that reduces the number of gate delays associated with the input signals. In a practical implementation, the XOR/SUMMER/MUX circuit includes XOR arrangements having a plurality of transistors implemented at a first transistor level and a plurality of transistors implemented at a second transistor level. The XOR/SUMMER/MUX circuit also includes transistors implemented at a third transistor level; these transistors are utilized by the multiplexer feature of the circuit.

Abstract: A method of processing data having one of four voltage levels stored in a DRAM cell is comprised of sensing whether or not the data voltage is above or below a voltage level midway between a highest and a lowest of the four levels, setting the voltage on a reference line higher than the lowest and lower than the next highest of the four levels in the event the data voltage is below the midway voltage level, and setting the voltage on the reference line higher than the second highest and lower than the highest of the four levels in the event the data voltage is above the midway point, and sensing whether the data voltage is higher or lower than the reference line, whereby which of the four levels the data occupies is read.