中英文资料外文翻译
31Digit, LCD/LED Display, A/D Converters 213digit 2
Abstract: The Intersil ICL7106 and ICL7107 are high performance, low power,
A/D converters. Included are seven segment decoders, display drivers, a reference, and a clock. The ICL7106 is designed to interface with a liquid crystal display (LCD) and includes a multiplexed backplane drive; the ICL7107 will directly drive an instrument size light emitting diode (LED) display.
The ICL7106 and ICL7107 bring together a combination of high accuracy, versatility, and true economy. It features autozero to less than 10μV, zero drift of less than 1μV/℃, input bias current of 10pA (Max), and rollover error of less than one count. True differential inputs and reference are useful in all systems, but give the designer an uncommon advantage when measuring load cells, strain gauges and other bridge type transducers. Finally, the true economy of single power supply operation (ICL7106), enables a high performance panel meter to be built with the addition of only 10 passive components and a display.
1Digit LCD/LED Display 2Keyword: 31 Features
A/D Converters
(1)Guaranteed Zero Reading for 0V Input on All Scales (2)1pA Typical Input Current
(3)True Differential Input and Reference, Direct Display Drive -LCD ICL7106, LED LCL7107
(4)Low Noise - Less Than 15μVP-P (5)On Chip Clock and Reference
(6)Low Power Dissipation - Typically Less Than 10mW
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(7)No Additional Active Circuits Required
2 Detailed Description
2.1 Analog Section
Figure 1 shows the Analog Section for the ICL7106 and ICL7107. Each measurement cycle is divided into three phases. They are (1) auto-zero (A-Z), (2) signal integrate (INT) and (3) de-integrate (DE).
FIGURE 1 ANALOG SECTION OF ICL7106 AND ICL7107
2.2 Auto-Zero Phase
During auto-zero three things happen. First, input high and low are disconnected from the pins and internally shorted to analog COMMON. Second, the reference capacitor is charged to the reference voltage. Third, a feedback loop is closed around the system to charge the auto-zero capacitor CAZ to compensate for offset voltages in the buffer amplifier, integrator, and comparator. Since the comparator is included in the loop, the AZ accuracy is limited only by the noise of the system. In any case, the offset referred to the input is less than 10μV.
2.3 Signal Integrate Phase
During signal integrate, the auto-zero loop is opened, the internal short is removed, and the
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internal input high and low are connected to the external pins. The converter then integrates the differential voltage between IN HI and IN LO for a fixed time. This differential voltage can be within a wide common mode range: up to 1V from either supply. If, on the other hand, the input signal has no return with respect to the converter power supply, IN LO can be tied to analog COMMON to establish the correct common mode voltage. At the end of this phase, the polarity of the integrated signal is determined. 2.4 De-Integrate Phase
The final phase is de-integrate, or reference integrate. Input low is internally connected to analog COMMON and input high is connected across the previously charged reference capacitor. Circuitry within the chip ensures that the capacitor will be connected with the correct polarity to cause the integrator output to return to zero. The time required for the output to return to zero is proportional to the input signal. Specifically the digital reading displayed is:
?VIN?DISPLAY COUNT=1000?V?REF2.5 Differential Input
??? ?The input can accept differential voltages anywhere within the common mode range of the input amplifier, or specifically from 0.5V below the positive supply to 1V above the negative supply. In this range, the system has a CMRR of 86dB typical. However, care must be exercised to assure the integrator output does not saturate. A worst case condition would be a large positive common mode voltage with a near full scale negative differential input voltage. The negative input signal drives the integrator positive when most of its swing has been used up by the positive common mode voltage. For these critical applications the integrator output swing can be reduced to less than the recommended 2V full scale swing with little loss of accuracy. The integrator output can swing to within 0.3V of either supply without loss of linearity.
2.6 Differential Reference
The reference voltage can be generated anywhere within the power supply voltage of the converter. The main source of common mode error is a roll-over voltage caused by the
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