电话系统智能去电控制器的设计(论文+电子通信类英文文献翻译) 第4页
× lower input bias current thanks to processing. Feedback through the Q1-A1-R1 loop and the Q2-A2-R2 loop maintains constant collector current of the input devices Q1 and Q2, thereby impressing the input voltage across the external gain setting resistor RG. This creates a differential gain from the inputs to the A1/A2 outputs given by G = (R1 + R2)/RG + 1. The unity-gain subtractor, A3, removes any common-mode signal, yielding a single-ended output referred to the REF pin potential. The value of RG also determines the transconductance of the preamp stage. As RG is reduced for larger gains, the transconductance increases asymptotically to that of the input transistors. This has three important advantages: (a) Open-loop gain is boosted for increasing programmed gain, thus reducing gain related errors. (b) The gain-bandwidth product (determined by C1 and C2 and the preamp transconductance) increases with programmed gain, thus optimizing frequency response. (c) The input voltage noise is reduced to a value of 9 nV/Hz, determined mainly by the collector current and base resistance of the input devices. The internal gain resistors, R1 and R2, are trimmed to an absolute value of 24.7 kΩ, allowing the gain to be programmed accurately with a single external resistor.
7.6 Other fields
Instrumentation amplifiers like This new microcontroller offer high CMR, which is a measure of the change in output voltage when both，inputs are changed by equal amounts. These specifications are usually given for a full-range input voltage change and a specified, source imbalance. For optimal CMR ,the reference terminal should be tied to a low，impedance point, and differences in capacitance and resistance，should be kept to a minimum between the two inputs. In many applications shielded cables are used to minimize noise, and for best CMR over frequency the shield should be properly driven. The capacitances of input cable shields, thus minimizing the capacitance mismatch between the inputs. Since This new microcontroller output voltage is developed with respect to the potential on the reference terminal, it can solve many grounding problems by simply tying the REF pin . To isolate low level analog signals from a noisy digital environment, many data-acquisition components have separate analog and digital ground pins. It would be convenient to use a single ground line; however, current through ground wires and PC runs of the circuit card can cause hundreds of errors. Therefore, separate ground returns should be provided to minimize the current flow from the sensitive points to the system ground. These ground returns must be tied together at some point, usually best at the ADC package
8. Conclusion
As described in this paper, the Closed Caption system that utilizes these microcontroller and Front End LSI can provide stable data reception and implementation. Utilizing a Display RAM of a single port RAM structure with full-screen capability by special implementation, these microcontrollers have overcome the problems that dual port structure Display RAM has. The single port Display RAM enabled to support full-screen capability with less space and low cost. The program is now much easier by full-screen Display RAM capability. The high performance of these microcontrollers make us believe that our consideration which regards the Text mode as a new information medium, which will benefit all the viewers. This advantage allows easy visual operation in the OSD menu system for all types of TV receivers.
Regardless of the system in which it is being used, This new microcontroller provides greater accuracy at low power and price. In simple systems, absolute accuracy and drift errors are by far the most significant contributors to error. In more complex systems with an intelligent processor, an autogain/autozero cycle will remove all absolute accuracy and drift errors, leaving only the resolution errors of gain, nonlinearity, and noise, thus allowing full 14-bit accuracy.From: study of microcontroller （Canada）2002, vol 3 ,43-50
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