Abstract: Multiple controllable delays reduce EMI radiated during the transmission of multiple synchronized signals. Each controllable delay introduces a controlled delay into a corresponding signal being transmitted. The controlled delay is such that the combined strength of the multiple signals at peak frequencies is substantially reduced. This results in reduced EMI radiation at those peak frequencies.

Abstract: A system (50) has a shifting delay circuit (60) which provides a variable delay for delaying a source clock and a delay locked loop (DLL) (70) which includes a delay line (72) which provides a variable delay for delaying the source clock. The delay line (18) has its delay varied by a counter (74). The counter (74) is incremented in order to change the delay. The shifting delay circuit (60) is based on half periods of a reference clock (GCLK) which has a known relationship to the source clock. The total delay for the source clock is a combination of that provided by shifting delay circuit (60) and delay line (72). The delay line (72), which requires relatively large amounts of die area in an integrated circuit can be smaller in size due to the usage of shifting delay circuit (60).

Abstract: Described is a variable digital delay cell with a first input for receiving a first input signal to be delayed, a first output for providing a first output signal which is delayed with respect to the first input signal, and a control signal for controlling the delay time of the delay cell. The delay cell further includes a second input for receiving a second input signal which is delayed with respect to the first input signal, and a second output for providing a second output signal which is delayed with respect to the first input signal by a fixed delay time. The delay cell according to the invention can be driven as a single device, but also allows a cascading of an `unlimited` number of delay cells without increasing the base delay in comparison to a single delay cell.

Abstract: An integrated delay line calibration method and apparatus are provided for a direct access storage device (DASD). A delay line, such as used in a direct access storage device (DASD) is calibrated by configuring the delay line as a ring oscillator for calibration. A delay line ring frequency is compared to a reference frequency. The delay of the delay line is adjusted until the delay line ring frequency and the reference frequency are equal. Each delay block within the delay line is controlled by a delay adjust digital-to-analog converter (DAC). A control logic circuit couples N-bit words to the delay adjust digital-to-analog converter (DAC) for calibration adjustment of the delay line delay.

Abstract: A logic analyzer uses a single tapped delay line and a single array of sampling cells for high speed digital signal acquisition, by controlling both edges of a substantially 50% duty cycle clock signal to drive a delay line buffer chain. The chain operates continuously; there being no need for interruptions for precharge intervals. Thus, the need for a second delay line buffer chain is eliminated.

Abstract: A programmable phase adjuster spans a clock signal's period with N linearly distributed phase steps. The resulting phase adjust resolution is finer than that of an inverter delay for a given process. Enhancement of the phase resolution of a phase picker CRM architecture enables use of the architecture for recovering clock signals from high data rate data streams in a way that minimizes power and area and allows optimization for multi-channel applications.

Abstract: A time delay generator (20) includes a threshold generator (30), a ramp generator (32) and a comparator (34). The threshold generator provides a fixed threshold at one input of the comparator while the ramp generator provides at the other input a ramp signal whose slope is programmable. The ramp generator includes current switches (86 and 90) and a current converter (74). In response to input and range signals, the current switches provide a programmed input current and a programmed range current. The current converter generates a ramp current that is proportional to the range current and inversely proportional to the input current and couples that ramp current to an integrating ramp capacitor. The structure of the time delay generator facilitates noise filtering of the threshold signal and positioning of the threshold signal away from ramp nonlinearities.

Abstract: A delay circuit for delaying high-speed logic signals has a continuously-variable delay which is a linear function of a control current. The resulting delay time may be set as short as a single logic gate delay. The CMOS delay circuit comprises delay means having as its output an internal signal characterized by an internal signal swing, coupled to amplifier means whose output is the delayed logic signal, characterized by a settling time. The amplifier means contributes minimal delay. The swing of the internal signal of the delay circuit is controlled by differential negative feedback to be just sufficient to drive the next stage, while the delay circuit's settling time is controlled by capacitively coupled positive feedback to be as short as the delay itself. The differential negative feedback is provided by four MOS devices.

Abstract: An improved edge-triggered fully digital delay locked loop (DLL), which maintains reliable synchronization from startup and in spite of system clock jitter is described. An internal clock signal is synchronized with a reference clock signal by propagating the reference clock signal through a variable digital delay path. A wide phase detection region surrounds a selected rising edge of the internal clock signal. The DLL loop is open as long as the internal clock signal and a target edge of the reference clock signal are not simultaneously within the phase detection region. To achieve a DLL locked condition, the variable delay is increased from a minimum setting until the edge of the phase detection region is shifted in time just past the target edge of the reference clock. Once the DLL loop has been closed, a clock jitter filter is enabled to reject reference clock jitter effects on the DLL locked condition.

Abstract: A voltage-controlled oscillator has a feedback circuit connected to the gate of a transistor which controls a current flowing through an oscillation unit. The feedback circuit applies a voltage depending on the DC voltage of an oscillated signal to the gate of the transistor. When the oscillated signal is reduced in level to lower the DC voltage, the feedback circuit lowers the voltage applied to the gate of the transistor. The current flowing through the oscillation unit is reduced to increase the level of the oscillated signal. When the oscillated signal is increased to increase the DC voltage, the feedback circuit increases the voltage applied to the gate of the transistor. The current flowing through the oscillation unit is increased to reduce the level of the oscillated signal. The feedback process prevents the voltage-controlled oscillator from operating unstably regardless of manufacturing variations of transistors from design values.

Abstract: At least two level detectors compare a multilevel signal to respective prescribed voltage levels to produce corresponding streams of bits. These bit streams are repeatedly delayed in respective digital delay lines, and bits from the digital delay lines are output in parallel to multilevel decoder logic. The multilevel decoder logic converts the parallel bits into a plurality of corresponding two-level decoded bits and performs error detections for an invalid transition in the multilevel signal. The decoded bits may be descrambled and block decoded.

Abstract: A digital delay lock loop (DLL) circuit for clock signals with reduced delay line length includes a first phase difference detector for detecting a first phase difference, and a second phase difference detector for detecting a second phase difference. The circuit further includes an inverter for inverting an input clock signal, and a switch controlled by the second phase difference detector for switching between the input clock signal and the inverted input clock signal in accordance with the second phase difference to provide a clock signal to the first phase difference detector. In a method aspect, a method for reducing delay line length in a digital delay locked loop (DLL) includes determining a phase difference between an input clock signal and a feedback clock signal, and maintaining the phase difference between the input clock signal and the feedback clock signal within approximately 180.degree..

Abstract: A delay signal generating apparatus incorporated in an integral circuit, includes a plurality of serially-connected delay elements for delaying an input signal successively and for outputting plural delay signals, a heat generating circuit for heating the plurality of delay elements, and a heat controller for controlling a heat amount generated by the heat generating circuit so as to change the delay time of each of the plural delay signals.

Abstract: A fractional period delay circuit to delay a clocking signal by a non-integer fraction of the period of the clocking signal is disclosed. The fractional period delay circuit has a first delay line connected to a master timing signal to delay the master clock to form the first timing signal. The fractional period delay circuit has plurality of adjustable delay lines. Each adjustable delay line is connected to the master timing signal to delay the master timing A delay adjustment input will modify the delay of the adjustable delay circuit. The fractional period delay circuit further has a plurality of phase difference detectors connected to the output of the first delay line and to the output of one of the plurality of adjustable delay lines. The phase difference detector will create a difference signal indicating a difference in phase between the first timing signal and one of the delayed timing signals. A plurality of sequence timing signals are created in a is timing sequence generator.

Abstract: A voltage controlled oscillator (VCO), for use in a phase locked loop for clock multiplication, for example in recovery of data pulses from a data stream input comprising digital data with unknown phase. According to the invention, the VCO comprises a plurality of VCO stages, each stage being implemented as a differential amplifier. The amplifier load is formed of two cross-coupled gate devices and of two gate devices which are connected as diodes. The differential input is applied to a source coupled input pair as well as to two pull-down gate devices.

Abstract: A delay circuit is to produce a delay timing which is larger than one cycle time of a reference clock while the resolution of which is smaller than the one cycle time of the reference clock.

Abstract: A clock compensation circuit includes a clock tree; a reference clock; a phase detector for detecting relative phase information of the tree clock and the reference clock; a controller, coupled to said phase detector, for determining and controlling the amount of delay necessary to shift the output of the clock tree in phase with the reference clock; and a programmable delay logic coupled to said controller. The programmable delay logic comprises a string of delay elements that selectively participate in a delay string for shifting the tree clock in phase with the reference clock.

Abstract: An apparatus for and method of reducing electromagnetic interference of an integrated circuit by providing multiple choking levels are disclosed. A choking circuit includes a choking level select signal generator, a pulse choking circuit connected to the choking level select signal generator, and a modulation control circuit connected to the pulse choking circuit. The choking level is increased when modules of the integrated circuit are less active, which reduces electromagnetic interference. The choking level is decreased when modules of the integrated circuit are more active, which maintains the voltage supplied to the power bus above a desired level.

Abstract: It is an object to obtain a semiconductor device capable of changing a delay time of an output signal of a PLL circuit with respect to an external clock signal after installed in a system. An external clock signal is inputted to an input terminal (1.) An address value is inputted to an input terminal (3.) A decoder (9) selects one of a plurality of delay times in a voltage-controlled oscillator (8) according to the address value. The phase of a signal outputted to an output terminal (2) is delayed with respect to the external clock signal at the input terminal (1) by the delay time selected. Accordingly, it is possible to change the delay time of the output signal of the PLL circuit with respect to the external clock signal after installation in a system.

Abstract: A power management system pad clock and self-test circuit includes a clock processing circuit having a input configured to receive an oscillator clock signal having a first frequency. The clock processing circuit is configured to generate a first pad clock signal having a frequency approximately equal to one-half the first frequency and a second pad clock signal having a frequency that is equal to a programmable fraction of the first frequency. The circuit also includes a main pad clock output node. Multiplexer circuitry is coupled to the clock processing circuitry and the main pad clock output node and configured to receive a plurality of peripheral signals. The multiplexer circuitry is configured to operate in a standard mode of operation wherein one of the first pad clock signal and the second pad clock signal is routed to the main pad clock output node and a first test mode of operation wherein one of the plurality of peripheral signals is selectably routed to the main pad clock output node.

Abstract: A system and method for generating and optimizing clock signals with non-overlapping edges on a chip using a unique programmable on-chip clock generator. Overlapping of the edges of the clocking signals is avoided by adjusting an amount of delay introduced in the on-chip clock generator circuit. The amount of delay is adjusted by programming the on-chip clock generator using either hardware and/or software programming. In hardware programming, the amount of delay adjusted by physically altering the composition of delay elements in the on-chip clock generator. In software programming, the delay is adjusted using software commands to control the operation of delay elements in the on-chip clock generator, or to select the paths that delay the signals.

Abstract: A circuit is designed with a reference circuit (200) for generating a reference signal. The reference signal determines a reference period. A delay circuit (208, 212, 216) responsive to the reference signal produces a delay signal. A control circuit (248, 254, 258, 260, 262) responsive to the delay signal produces a control signal. The delay circuit emulates the speed of an integrated circuit for the reference period. Control signals from the control circuit compensate the integrated circuit performance for measured circuit speed variations.

Abstract: A signal detection circuit employs a delay line with edge detection logic for capturing and buffering timing information about an input signal. A plurality of comparators for comparing the input signal to different reference potentials capture amplitude information in the input signal launching bits into respective delay lines. Preferably, each delay line includes a counter for counting detected bit edges.

Abstract: Digital signal delay lines with electrically programmable and trimmable delay times, including electrically erasable and reprogrammable delay times. Floating gate field effect transistors are programmed to select current, capacitance, and/or threshold and thereby set a delay time determined by acurrent charging of a capacitor up to a threshold voltage. Trimming after packaging avoids package offsets. Temperature and power supply voltage compensation by current combining gives compensation compatible with the electrical programming.

Abstract: A scale of circuit is reduced when a plurality of variable delay circuits are provided with respect to the same signal. A variable delay circuit is constructed such that variable delay circuit elements each comprising a delay circuit element composed of buffer gates each having an identical amount of delay connected in series and a selector e for selecting the input and output of the delay circuit element are connected in series in n-1 stages, wherein the number of the delay elements of the delay circuit element in each variable delay circuit element is 2.sup.i-1 (i: number of stages) in the order from the final stage.

Abstract: An input signal and a signal obtained by delaying that input signal are compared, an output signal is produced based on the amount of the delay, and the output signal is used to form a control signal by a low pass filter. The delay of the input signal is controlled so as to produce a plurality of stable clocks and enable stable high speed signal processing without raising the clock frequency.

Abstract: A circuit and method for deskewing signals by using cross power supply logic paths to compensate for delays created by power supplies operating at different voltages. A first replica circuit operating at a first supply voltage is placed in series with a first signal operating at a second supply voltage. A second replica circuit operating at the second supply voltage is placed in series with a second signal having a skew difference from the first signal and operating at the first supply voltage. The replica circuits generally have a scale factor which is generally a fraction of the equivalent driver circuits associated with the particular output signals. As a result, the present invention will deskew arbitrary power supply differences. By matching delays, the replica and true circuits provide the same delay. As a result, the sum of the delays for all the blocks in each path will be constant which maintains a desired skew difference between the output signals.

Abstract: A multi-stage apparatus used as a voltage controlled oscillator. Each stage includes a first complementary differential current switch and a second complementary differential current switch with a second set of complementary differential current switches having a first complementary differential current switch and a second complementary differential current switch, the two sets of complementary differential current switches are connected in a push pull arrangement. In this arrangement, the outputs of the first complementary differential current switch of the first set of complementary differential current switches and the first complementary differential current switch of the second set of complementary differential current switches are connected with the input of the second complementary differential current switch of the first set of complementary differential current switches.

Abstract: Integrated circuits must fulfill published timing specifications that have been given to customers. To fulfill published timing specifications, such as minimum valid time and maximum valid time, a circuit for adjusting the output signals from an integrated circuit is introduced. The circuit comprises in part a speed detector circuit that determines the speed of a clock signal. The speed detector circuit outputs a speed signal that defines how fast the integrated circuit is operating. The speed signal is passed to a speed adjustment circuit. The speed adjustment circuit delays, as appropriate, output signals from the integrated circuit. The output signals are delayed such that output signals fulfill the timing, specifications published in the data book for this integrated circuit. The speed adjustment circuit delays output signals by adding buffers along the data path which add propagation delay to the output data path.

Abstract: An output driver circuit comprises a plurality of parallel pull up and pull down circuits each comprising at least one transistor switch switchable between on and off states and circuitry operable to maintain a desired resistance in the circuit when the transistor switch is switched on, and switch actuating circuitry including time delay circuitry for effecting a sequence of transistor switching operations in said pull-up and pull-down circuits with a time delay between successive operations, each operation effecting simultaneous switching of a transistor in one pull-up circuit and one pull-down circuit, whereby the output impedance is stabilised during a change in signal on the output terminal.

Abstract: It is an object to provide a signal delay computing method for efficiently improving the accuracy of signal delay values. First, a space (SPi) including a load capacitance value (C1), a load resistance value (R1) and a transition delay value (D0) is selected. Next, eight vertexes (u1 to u8) of the space (SPi) are extracted. The vertex uk (k=1 to 8) is represented by coordinates as (C1.sub.uk, R1.sub.uk, D0.sub.uk, D1.sub.uk). The combination of these values about one vertex are known by circuit simulation. Next, substitution of the values of the coordinates into a delay computing equation is performed in order for all of the integers k=1 to 8. Then eight simultaneous equations are obtained. The simultaneous equations are solved to determine the values of the coefficients (W.sub.0i to W.sub.7i) in the delay computing equation. The coefficients (W.sub.0i to W.sub.

Abstract: A circuit for synthesizing, from a first signal having a first frequency, a second signal having a second frequency. This synthesis includes using a delay locked loop in combination with a minimal amount of logic circuitry to generate a synthesized output signal which is completely deterministic and does not require any analog control.

Abstract: A clock generating circuit includes a plurality of delay lines connected in cascade, each delay line including two switching elements for letting in or shutting out a clock, and a delay element connected to each of the switching elements. A PLL circuit and a semiconductor device both include the clock generating circuit. The number K of the delay units in each of the delay lines of the clock generating circuit is calculated from:K>?{1/(2.multidot.N.multidot.F.sub.ref)}-(T.sub.mul)!/(T.sub.

Abstract: A method and circuit for generating a selectively variable clock signal from one of 256 frequencies within a specified range from two fixed frequency oscillator source signals is provided. The method and circuitry maintain a substantially fifty-percent duty cycle in the output clock signal.

Abstract: An apparatus and method for instantaneously stretching multi-phase clock signals includes a delay line to generate a plurality of multi-phase clock signals. An instantaneous signal stretch logic circuit is connected to the delay line. The instantaneous signal stretch logic circuit transforms the plurality of multi-phase clock signals into stretched multi-phase clock signals in response to a filter capacitor analog signal and a digital stretch signal. Multiple embodiments of the instantaneous signal stretch logic circuit are disclosed. However, each embodiment includes dual current control paths with a single current control path responsive to the digital stretch signal, which is preferably a single bit value.

Abstract: Apparatus and method to logically process signals representative of multiple bits of multiple-bit numbers include successively delaying application of the bit-representative signals to logical processing stages from associated input registers by a delay interval between input registers that is substantially equal to the processing delay interval per bit-level processing stage. In this way, successively more significant bits of each of plural numbers being logically processed are validly available for processing at each bit-level logic stage after a delay that is substantially equal to the processing delay interval of a preceding bit-level logic stage.

Abstract: A digital delay line supplies from a periodic input signal n signals with the same period mutually shifted by one n-th of the input signal period. The digital delay line includes n cells, each of which includes m delay elements in series, each output of a delay element being connected to an input of a multiplexer. The output phase of the n-th cell is compared with that of the input signal phase. The output of a multiplexer of the n cells is modified after each comparison.

Abstract: A system for converting between parallel data and serial data is described. In the system (10), individual bits of the parallel data (12) are latched into individual registers (117). Each register (117) is coupled to a corresponding AND gate (110) which is also connected to receive phased clock signals. The output terminals of the AND gates (110) are connected to an OR gate (115). Using the system, with appropriately phased clocks, the parallel data is converted into serial data.

Abstract: A variable delay circuit capable of changing delay time includes a latch circuit constituted of a pair of inverters cross-coupled to each other and a transistor serving for reducing voltage difference between two inputs of the latch circuit based on a control signal given thereto. The control signal is also supplied to a pair of transfer gates to control the delay time of the variable delay circuit. The latch circuit has two inputs, between which the transistor is coupled, coupled to the respective transfer gates' ends, at which buffers are respectively coupled to feed output signals. When the control signal reaches a high level, the state of the transistor becomes one of low impedance, so that the voltage difference between the two inputs of the latch circuit is reduced, and so that the state of the latch circuit can be quickly and easily changed with little energy.

Abstract: A timing vernier produces a set of timing signals of similar frequency and evenly distributed in phase by passing an input reference clock signal through a succession of delay stages, each stage providing a similar signal delay. A separate one of the timing signals is produced at the output of each delay stage. The reference clock signal and timing signal output of the last delay stage are supplied as inputs to a phase lock controller through separate adjustable first and second delay circuits. The phase lock controller controls the delay of all stages so that the timing signal output of the last stage is phase locked to the reference clock. In accordance with the invention, the delays of the first and second delay circuits are adjusted to compensate for controller phase lock error.

Abstract: A variable delay circuit which includes a first power source line for supplying a first power source voltage, a second power source line for supplying a second power source voltage which is smaller than the first power source voltage, an input terminal for receiving an input signal, a selection terminal for receiving a selection signal, an output terminal for outputting an output signal which is delayed relative to the input signal, a pull-up circuit coupled between the first power source line and the output terminal for carrying out a pull-up operation based on the input signal which is received via the input terminal, and a pull-down circuit coupled between the output terminal and the second power source line for carrying out a pull-down operation based on the input signal which is received via the input terminal. The pull-up or pull-down circuit has a delay time which is variable in response to the selection signal which is received via the selection terminal.

Abstract: A variable delay circuit includes a gate chain of first to n-th delay gates (n is an integer larger than 2) connected in series to each other via delay gate wirings having respective wiring lengths, the first delay gate receiving an input signal for delay; first to n-th separator gates to which the outputs of the first to n-th delay gates are input, respectively; first to n-th separator gate wirings having wiring lengths successively shortened from the first to n-th separator gate, first ends respectively connected to the first to n-th separator gates, and second ends connected to an n:1 selector, for selecting one of the outputs of the first to n-th separator gates in according with a select signal, and a select signal generating circuit for controlling the n:1 selector. The variable delay circuit has no loss of resolution due to parasitic capacitance of the delay gate wirings.

Abstract: Digital signal delay lines with electrically programmable and trimmable delay times, including electrically erasable and reprogrammable delay times. Floating gate field effect transistors are programmed to select current, capacitance, and/or threshold and thereby set a delay time determined by acurrent charging of a capacitor up to a threshold voltage. Trimming after packaging avoids package offsets. Temperature and power supply voltage compensation by current combining gives compensation compatible with the electrical programming.

Abstract: A differential-type voltage-controlled oscillator (VCO) with low-frequency stability compensation is disclosed. The differential-type VCO comprises a voltage-to-current converter for converting an input voltage signal into a biasing current signal to control the frequency of the VCO output. The VCO further comprises a number of stages of differential amplifiers connected in cascade. Each of the stages of differential amplifiers includes a pair of differential input PMOS transistors, with each of the PMOS transistors connected to a pair of NMOS load transistors. Each of the pair of NMOS load transistors are connected in parallel. The VCO further comprises a number of stages of bias circuits connected in cascade. Each of the bias circuits is connected to a corresponding stage of the differential amplifiers for receiving the bias current generated by the voltage-to-current converter.

Abstract: A digital delay line supplies from a periodic input signal n signals with the same period mutually shifted by one n-th of the input signal period. The digital delay line includes n cells, each of which includes m delay elements in series, each output of a delay element being connected to an input of a multiplexer. The output phase of the n-th cell is compared with that of the input signal phase. The output of a multiplexer of the n cells is modified after each comparison.

Abstract: A bias voltage generator for a voltage controlled oscillator is described. In one aspect of the invention, the bias voltage generator includes a biasing circuit to generate a minimum clock output at zero operating voltage, and includes a common mode rejection circuit for the BIASN and BIASP control voltages for the differential delay stages and a IDD test current shut-down circuit. A differential delay stage is described that includes a current source controlled by the BIASN and BIASP control voltages from the bias voltage generator, a resistance linearization circuit for current controlling transistors of a BIASN circuit, and a process variation circuit for compensating for temperature and process variations. The improved characteristics of the resulting VCO permits high frequency operation with a relatively low gain, relatively constant gain throughout operating voltage range, improved noise rejection capabilities, increased speed of delay stage, and reduced output signal swing.

Abstract: A test configuration is provided which allows a plurality of variable delay units within a delay chain to be compared with respect to one another. The delay chain is employed within a clock generator circuit that generates internal clock signals of a microprocessor. During normal operation, a set of multiplexers interposed within the delay chain are configured such that the plurality of variable delay units are electrically coupled in series with respect to one another. During a test operation when it is desired to test the variable delay units for possible defects, the four delay units are electrically separated from one another by setting the multiplexers in a test mode. A common test signal is then driven through two or more of the variable delay units simultaneously, and a compare circuit coupled to the output of each variable delay unit determines whether a transition in the common pulse signal propagated through each variable delay unit at essentially the same time.

Abstract: A glitch filter for eliminating noise pulses less than 12 nanoseconds (ns) created by large devices on the SCSI bus and reflections of the 12 ns pulses created by a long SCSI bus cable, as well as noise pulses on the order of 35 ns typically found on a SCSI bus. The glitch filter includes a Schmitt trigger connected to receive the SCSI bus signal along with three filters connected in series with the Schmitt trigger. The first filter removes positive pulses having a pulse width less than 12 ns and provides an inverted output. The second filter removes negative pulses having a pulse width less than 12 ns and provides an inverted output. The third filter removes pulses having a pulse width less than 35 ns and provides the output of the glitch filter.

Abstract: First and second complementary input voltages control current flow through first and second switches (e.g. semiconductor devices) each respectively connected in first and second control circuits with a first constant current source. When the input voltages change, current starts to increase through one control circuit to produce increases in the voltage drop across an impedance (e.g. resistor) in such circuit. When a particular voltage difference is produced between the impedance voltage and an adjustable biasing voltage, a third switch (e.g. semiconductor device) closes to produce a first resultant voltage. The resultant delay in the third switch closure is dependent upon the adjustable magnitude of the biasing voltage. As the voltage increases across the impedance in the one control circuit, the voltage decreases across an impedance in the other control circuit, causing a second resultant voltage to be produced at a fourth switch (e.g. semiconductor device).

Abstract: In a display data driving IC for driving a matrix display unit, switching current in a plurality of channel driving buffer circuits is suppressed, and when a multi-tone display unit is driven, the tone display quality is improved.