Successive approximation type, integral type, voltage-frequency conversion type, etc., mainly used in medium speed or low speed, medium-accuracy data acquisition and
57 datasheet and intelligent instruments. Grade-and high-speed pipelined ADC is mainly used in the case of transient signal processing, storage and
57 price and fast waveform recording, high-speed data acquisition, signal quantification and
57 suppliers and high-speed digital video communication technology and other fields. In addition, the use of pulse-type and folded structure of the high-speed ADC, can be applied to the base-band broadcast satellite demodulation and so on. ~ type ADC is mainly used in high-precision data acquisition systems, especially digital audio, multimedia, seismic equipment, sonar and other electronic measurement. The following types of ADC for a brief introduction.
1) successive approximation
successive approximation ADC is proud of the module is widely used conversion method, which includes a comparator, a number of film converter, a successive approximation register (SAR) and a logic control unit. It is the sampled input signal voltage is constantly compared with the known, one clock cycle to complete a conversion, N-bit conversion takes N clock cycles, the conversion is complete, the output binary number. This type of ADC resolution and sampling rate are mutually contradictory, the higher the sampling rate is low resolution, to improve the resolution, the sampling rate will be limited.
advantages: less than 12 bit resolution, lower prices, the sampling rate of up to 1 Msps; compared with other ADC, power consumption is very low.
Disadvantages: higher than 14 bits of resolution in the case of higher prices; analog sensor signals generated during the conversion required before conditioning proud of, including gain stage and filtering, this will significantly increase costs.
2) Integrating ADC
integral, also known as dual-slope ADC ADC or slope ADC, its applications are more widespread. It consists of an input switch with an analog integrator, a comparator and a counter unit constituted by two points to convert the input analog voltage proportional to its average time interval. At the same time, in this time interval counter used to count the clock pulses to achieve the A / D converter Jue. Integrating ADC using two points of the time with a clock generator and counter to determine, so the resulting clock frequency of the D expression and independent of its conversion accuracy depends only on the reference voltage UR. In addition, the input side of the integrator, so the AC noise interference has a strong suppression. To suppress high frequency noise and fixed low-frequency interference (such as the 50 H or 60 Hz), suitable for noisy industrial environments. This type of ADC is mainly used in low-speed, precision measuring and other areas, such as a digital voltmeter.
advantages: high resolution, up to 22; low power consumption and low cost.
Disadvantages: low conversion rate, conversion rate of 12 when 100 ~ 300 bps.
3) side comparison A / D converter
side comparison ADC main features are speed, it is all the A / D converter in the fastest, the development of modern high-speed AD (Most of this structure, the sampling rate can reach more than 1 Gsps, but by the power and size constraints, parallel comparison AD (- high resolution is difficult to do.
all this structure of the ADC bit conversion simultaneously, the conversion time depends on the comparator switching speed, the encoder transmission time delay, etc. to increase the output code of the conversion time of less impact, but with the resolution of the increased demand for high-density analog designed to achieve the transformation necessary to the large number of precision voltage divider resistors and the comparator circuit output increase in the number one, would double the number of precision resistors, comparators are approximate doubling.
side comparison of the ADC resolution is limited by die size, input capacitance, power and other limited results if repeated in parallel comparator does not match the precision, can also cause static errors, such as input offset voltage will increase the same time, this type of As the sub-ADC comparator voltage, coding bubbles, there will be a discrete, inaccurate output, so-called "spark code".
Advantages: mold proud of the highest conversion speed.
Disadvantages: low resolution, power consumption and high cost.
4) voltage to frequency converter type ADC
voltage to frequency converter type ADC is an indirect type of ADC, it is the first analog signal input voltage into a pulse signal proportional to its frequency, and then in a fixed time interval to count this pulse signal, counting result is an analog voltage proportional to the input digital signal from the theory, the ADCs resolution rate can be increased indefinitely, as long as the use of a long time to meet the requirements of the output frequency resolution of the cumulative number of pulses the width of the brother.
advantages: high accuracy, lower prices, lower power consumption.
< br> Disadvantages: similar to the integral ADC, the conversion rate is limited, 12-bit time for the 100 ~ 300 sps.
5) a type of ADC
a ADC conversion device, also known as oversampling converter, which uses incremental encoding that is based on the previous value and the value of the latter to quantify the difference between the size of the code. a ADC includes an analog modulator and digital decimation filter. a major modulator sampling and completion of the incremental encoder signals, the digital decimation filter it to provide an incremental encoder that code; digital decimation filter code to complete the extraction of a filter to convert the incremental encoder high-resolution linear pulse code modulation digital signal. So in fact equivalent to a decimation filter pattern converter.
advantages: higher resolution, up to 24; conversion rate is higher than the voltage to frequency transformation type and integral type ADC; low price; internal use of high frequency over-sampling technology, a digital filter, reduces the sensor signal filtering requirements.
Disadvantages: high speed ADC a higher price; the conversion rate under the same conditions, than the integral ADC and successive approximation type ADCs high power consumption.
6) pipelined ADC
pipelined ADC, also known as sub-zone ADC, it is an efficient and powerful analog converter proud. Able to provide high-speed, high-resolution A / D conversion, and has a satisfactory low power consumption and small die size; through rational design, can also provide excellent dynamic performance.
pipelined ADC has a cascaded circuit of stem-level, each level includes a sample / hold amplifier, a low-resolution ADC and DAC, and a summing circuit, which also includes a summing circuit to provide gain The inter-stage amplifier. Fast and accurate spell-digital converter into two or more sub-areas (line) to complete. First-stage circuit T / sampling the input signal after the first by a coarse resolution, excellent bit A / D converter input to quantify, then at least use a spell-bit accuracy of product type D / A converter (MDAC) have a corresponding quantitative results of A / to be level and sent to the summing circuit, summing circuit to deduct this from the analog input signal level. The difference between a fixed and precise amplification gain of the circuit after the customs handed down a deal. After this treatment at all levels, from a high-precision K-bit fine A / D converter for converting the residual signal. The above levels of coarse and fine A / D output combined to constitute a high-precision curse-bit output.
Advantages: good linearity and low offset; can handle multiple samples simultaneously, a higher signal processing speed, typical for the
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Disadvantages: reference circuit and the bias structure is too complex; input signals require special handling, so that water passes through several levels caused by the delay circuit; of the latch timing demanding; demanding on the circuit technology, circuit board designed to be unreasonable will affect the linear gain, offset and other parameters.
At present, this new ADC architecture is mainly used for the THD and SFDR and other special housing requirements of high-frequency domain communication systems, noise, bandwidth and speed time-domain transient response characteristics of higher The CCD imaging system, the time-domain and frequency domain parameters are demanding data acquisition system.