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CA5130A Folha de dados(PDF) 8 Page - Intersil Corporation |
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CA5130A Folha de dados(HTML) 8 Page - Intersil Corporation |
8 / 19 page 8 transistors Q8,Q12 goes essentially to zero. The two preceding stages in the CA5130, however, continue to draw modest supply current (see the lower curve in Figure 16) even though the output stage is strobed off. Figure 1A shows a dual supply arrangement for the output stage that can also be strobed off, assuming RL = ∞, by pulling the potential of Terminal 8 down to that of Terminal 4. Let it now be assumed that a load resistance of nominal value (e.g., 2k Ω) is connected between Terminal 6 and ground in the circuit of Figure 1B. Let it further be assumed that the input terminal bias (Terminals 2 and 3) is such that the output terminal (No. 6) voltage is at V+/2. Since PMOS transistor Q8 must now supply quiescent current to both RL and transistor Q12, it should be apparent that under these conditions the supply current must increase as an inverse function of the RL magnitude. Figure 22 shows the voltage drop across PMOS transistor Q8 as a function of load current at several supply voltages. Figure 15 shows the voltage transfer characteristics of the output stage for several values of load resistance. Wideband Noise From the standpoint of low noise performance considerations, the use of the CA5130 is most advantageous in applications where the source resistance of the input signal is on the order of 1M Ω or more. In this case, the total input referred noise voltage is typically only 23 µV when the test circuit amplifier of Figure 2 is operated at a total supply voltage of 15V. This value of total input referred noise remains essentially constant, even though the value of source resistance is raised by an order of magnitude. This characteristic is due to the fact that reactance of the input capacitance becomes a significant factor in shunting the source resistance. It should be noted, however, that for values of source resistance very much greater than 1M Ω, the total noise voltage generated can be dominated by the thermal noise contributions of both the feedback and source resistors. Typical Applications Voltage Followers Operational amplifiers with very high input resistances, like the CA5130, are particularly suited to service as voltage followers. Figure 3 shows the circuit of a classical voltage follower, together with pertinent waveforms using the CA5130 in a split supply configuration. A voltage follower, operated from a single supply, is shown in Figure 4, together with related waveforms. This follower circuit is linear over a wide dynamic range, as illustrated by the reproduction of the output waveform in Figure 4A with input signal ramping. The waveforms in Figure 4B show that the follower does not lose its input-to-output phase sense, even though the input is being swung 7.5V below ground potential. This unique characteristic is an important attribute in both operational amplifier and comparator applications. Figure 4B also shows the manner in which the CMOS output stage permits the output signal to swing down to the negative supply rail potential (i.e., ground in the case shown). The digital-to- analog converter (DAC) circuit, described in the following section, illustrates the practical use of the CA5130 in a single supply voltage follower application. 9-Bit CMOS DAC A typical circuit of a 9-bit Digital-to-Analog Converter (DAC) (see Note) is shown in Figure 5. This system combines the concepts of multiple switch CMOS lCs, a low cost ladder network of discrete metal-oxide film resistors, a CA5130 op amp connected as a follower, and an inexpensive monolithic regulator in a simple single power supply arrangement. An additional feature of the DAC is that it is readily interfaced with CMOS input logic, e.g., 10V logic levels are used in the circuit of Figure 5. NOTE: “Digital-to-Analog Conversion Using the Intersil CD4007A CMOS lC”, Application Note AN6080. 3 2 1 8 4 7 6 + - Rs 1M Ω 47pF -7.5V 0.01 µF +7.5V 0.01 µF NOISE VOLTAGE OUTPUT 30.1k Ω 1k Ω BW (-3dB) = 200kHz TOTAL NOISE VOLTAGE (REFERRED TO INPUT) = 23 µV (TYP) FIGURE 2. CA5130 OUTPUT STAGE IN DUAL AND SINGLE POWER SUPPLY OPERATION CA5130, CA5130A |
Nº de peça semelhante - CA5130A |
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Descrição semelhante - CA5130A |
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