A digital to analog converter (DAC) is typically composed of several DAC elements, which receive digital input data and generate element signals according to the digital input data. The element signal can be voltage type or current type. Then, a signal integrator adds the element signals outputted from the DAC elements and generates an analog output signal. Digital-to-analog converters convert digital input signals to corresponding analog output signals. In operation, an internal reference signal (e.g., a reference current) is mirrored to form a plurality of currents which flow through switches that respond to a digital input signal. The combined currents thus form an analog output current signal that has thereby been converted from the digital input signal. D/A converters are used in many different kinds of systems such as modern process control systems to supply control signals to process valves, drive motors, and actuators. Digital-to-analog converters are particularly important in radar and communications systems, where transmitters must often transmit relatively high radio frequency (RF) signals derived from relatively low-speed digital signals. In digital communication systems such as a code division multiple access (CDMA) system, a time division multiple access (TDMA) system, and a frequency division multiple access (FDMA) system, a digital signal is modulated and the modulated digital signal is then converted into an analog signal as an output signal of baseband circuits at the baseband final stage. In direct digital synthesis (DDS), desired signal behaviour is achieved by converting digital phase data or other variable data to digital amplitude data, for instance by means of look-up tables. The digital amplitude data can then be converted to an analog amplitude by a digital-to-analog converter, or the amplitude data can be further used e.g. for signal phase or frequency processing. In general equipment such as a digital video camera apparatus, digital video signal data may be output as an analog video signal. In this case, the digital video camera apparatus may employ a D/A converter for converting digital luminance signal data of the digital video signal into an analog luminance signal in addition to a D/A converter for converting digital chrominance signal data into an analog chrominance signal. Digital to analogue converters usually include systems that incorporate a resister ladder, elements of which are selectively energized in response to the input digital signal value to yield a total output analogue signal of an appropriate size. Digital to analogue converters also utilize pulse width modulation (PWM) techniques to perform digital to analogue conversion. With these PWM techniques, a pulse width modulated signal is generated with a duty cycle controlled by the input digital signal value. This pulse width modulated signal is then low pass filtered and an analogue signal is produced with a value dependent upon the duty cycle of the pulse width modulated signal. s

Analog/digital converters are electronic circuits that convert an analog input signal into a digital output signal. A/D converters have various circuit configurations which may be used such as, for example, a sequential-comparative type, a serial-parallel type and an all-parallel type. These circuit configurations, respectively, have advantages and disadvantages with respect to conversion speed, conversion precision and the power consumption thereof. General types of A/D converters include comparator (flash) converters, successive approximation converters, and counting converters. Major factors that determine the quality of an A/D converter include the analog signal range, input impedance, sampling rate, accuracy, stability, conversion time, power consumption, and space requirements on an integrated circuit chip. Among converters for converting an analog signal into a digital signal, a subranging type A/D converter apparatus is to execute an A/D conversion by separating the A/D conversion into an A/D conversion of high-order bits and an A/D conversion of low-order bits. Successive approximation A/D converters are useful a wide range of applications, including data acquisition, test equipment, instrumentation, cellular communications, among others. The basic successive approximation A/D converter (ADC) includes an analog comparator and a clocked feedback loop having a successive approximation register (SAR) and a digital to analog converter (DAC). In the successive approximation signal converting, the data bits of the digital output signal are successively determined one after the other in successive approximation steps. To such an end, the analog/digital converter is provided with a comparator, a digital/analog converter DAC, a successive approximation register SAR, and a logic circuit. Of the above-mentioned three types of A/D converters, the all-parallel A/D converter exhibits the best conversion speed. The all-parallel circuit configuration is a basic configuration for an A/D converter implemented as an integrated circuit. However, the all-parallel circuit configuration has several disadvantages in that the conversion precision and the power consumption thereof are not sufficiently satisfactory.

Analog-to-digital (A/D) converters are used in a variety of applications whenever an analog input signal must be converted into a digital output signal. A/D converters are crucial devices to the digital signal processing, to have faster speeds, broader bandwidths, and lower power consumption. In the information and communication field, signal processing has demanded digital processing, faster speeds, and broader bandwidths, and information and communication devices have required reduced sizes and weight. In a digital communication system such as a wireless system or a VoIP system, an audio signal may be processed by a series of speech encoders and decoders as it is transmitted from one endpoint to another. When an analog signal converter is used in the mobile communication system, for example, cellular phones, signals to be transmitted are modulated into signals within a frequency band used in radio communication by a digital modulator. Signals of a predetermined frequency band are extracted through the digital filter. The signals are supplied to a digital-analog converter (DAC) through signal lines and are then sampled using sampling clock. The sampled digital signals are converted into analog signals. The converted analog signals are then supplied to a radio-frequency (RF) circuit through a smoothing filter. In general, when an analog signal is encoded and converted into a digital signal, processing such as sampling and quantization for converting an amplitude value of the signal into a discrete value is carried out. In implementing the sampling, a pulse generated at a constant cycle is used, wherein the cycle is called the sampling frequency. The analog and digital circuits are generally designed as different functional blocks. The analog block is connected to the digital block by the signal lines for transferring digital signals and a signal line for transferring sampling clock to sample the digital signals supplied to the DAC through the signal lines. Various components in A/D converters employ operational amplifiers, each of which serves a very important function. Operational amplifiers incorporated in A/D converters include a comparator, which compares a supplied analog input voltage with a reference voltage, a sample-and-hold circuit, which performs a sampling and holding operation of an input signal in order to achieve a faster speed and a broader bandwidth, a differential signal amplifier circuit, which is used for the signal amplification in a pipeline A/D converter.

A video converter receives an input video signal and converts it to an output video signal. In the process, the converter may have to change several aspects of the input video signal including the color encoding scheme, the pixel dimensions of the images, the manner in which the pixel data is encoded into the video signal and the subcarrier frequency. A digital display unit typically receives an analog display signal (e.g., in RGB format) and generates an image encoded in the analog display signal. Digital display units are characterized by discrete points (termed pixels) on a display screen usually contained in each digital display screen. Each point is generally actuated to a varying degree as determined by a received analog display signal. Such actuation generates an image encoded in the received analog display signal. Analog display signals usually contain multiple frames, with each frame containing multiple horizontal lines. Each display signal frame typically represents an image to be displayed on a digital display screen at a given instance in time. Digital displays often contain an analog to digital converter (ADC) to sample each display signal frame. Usually, video images output from a personal computer are displayed on a dedicated monitor by feeding R, G, and B signals and horizontal and vertical synchronizing signals from the personal computer directly to the monitor. The R, G, and B signals output from the personal computer are individually converted into digital signals by an analog-to-digital converter (A/D converter). These digital signals are temporarily stored in a line buffer. The digital signals stored in the line buffer are individually converted into analog signals by a digital-to-analog converter (D/A converter), and are then fed to an encoder for analog signal processing.

In the field of wireless communication devices, significant efforts are being made to use digital signal processing techniques to perform many of the signal processing tasks more commonly performed with analog circuitry. For example, it is necessary to convert an analog signal derived from a received radio frequency (RF) signal to a digital signal so that subsequent filtering and demodulating tasks can be performed digitally. Radio-frequency receivers (RF receivers) operate in analog mode in the RF receiving part. A received signal is only digitized after it has been mixed down into the baseband or an intermediate frequency. AGC (automatic gain control) circuits are used to regulate the signal level fed to the analog/digital converter (A/D converter), provided in the receiver for digitization, in such a way that the A/D converter is not overloaded. Mixed-signal systems are those that contain both analog and digital signals. Such systems often have unwanted crosstalk between the two domains. Crosstalk is defined as undesired noise appearing in one signal path as a result of coupling from another signal path. An analog-to-digital converter (ADC) is an example of a mixed-signal system that is subject to crosstalk interference. Standard measures taken to minimize crosstalk include shielding and supply isolation, clock dithering, differential inputs and outputs, optimizing the phase of the digital transitions, and adjustment of signal levels and slew rates to minimize either the receiver sensitivity or the transmitter power.