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AD624SD データシート(PDF) 11 Page - Analog Devices |
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AD624SD データシート(HTML) 11 Page - Analog Devices |
11 / 15 page REV. C AD624 –11– By establishing a reference at the “low” side of a current setting resistor, an output current may be defined as a function of input voltage, gain and the value of that resistor. Since only a small current is demanded at the input of the buffer amplifier A2, the forced current IL will largely flow through the load. Offset and drift specifications of A2 must be added to the output offset and drift specifications of the IA. PROGRAMMABLE GAIN Figure 38 shows the AD624 being used as a software program- mable gain amplifier. Gain switching can be accomplished with mechanical switches such as DIP switches or reed relays. It should be noted that the “on” resistance of the switch in series with the internal gain resistor becomes part of the gain equation and will have an effect on gain accuracy. A significant advantage in using the internal gain resistors in a programmable gain configuration is the minimization of thermo- couple signals which are often present in multiplexed data acquisition systems. If the full performance of the AD624 is to be achieved, the user must be extremely careful in designing and laying out his circuit to minimize the remaining thermocouple signals. The AD624 can also be connected for gain in the output stage. Figure 39 shows an AD547 used as an active attenuator in the output amplifier’s feedback loop. The active attenuation pre- sents a very low impedance to the feedback resistors therefore minimizing the common-mode rejection ratio degradation. Another method for developing the switching scheme is to use a DAC. The AD7528 dual DAC which acts essentially as a pair of switched resistive attenuators having high analog linearity and symmetrical bipolar transmission is ideal in this application. The multiplying DAC’s advantage is that it can handle inputs of either polarity or zero without affecting the programmed gain. The circuit shown uses an AD7528 to set the gain (DAC A) and to perform a fine adjustment (DAC B). VDD GND 225.3 124 4445.7 80.2 50 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 10k 20k VB 20k 10k 10k 50 –VS +VS 1 F 35V –IN +IN 10k 10k INPUT OFFSET NULL OUTPUT OFFSET NULL 10k TO –V (+INPUT) (–INPUT) VOUT 39.2k WR A4 A3 A2 A1 VSS 1k 10pF +VS 28.7k 316k 1k 1k –VS AD624 AD7590 AD711 Figure 39. Programmable Output Gain 225.3 124 4445.7 80.2 50 G = 100 K1 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 10k 20k VB 20k 10k 10k 50 –VS +VS 1 F 35V –IN +IN R2 10k R1 10k INPUT OFFSET TRIM OUTPUT OFFSET TRIM RELAY SHIELDS G = 200 K2 G = 500 K3 D1 D2 D3 Y0 K2 K3 74LS138 DECODER 7407N BUFFER DRIVER A B Y1 Y2 INPUTS GAIN RANGE +5V 10 F C1 C2 K1 – K3 = THERMOSEN DM2C 4.5V COIL D1 – D3 = IN4148 ANALOG COMMON GAIN TABLE A B GAIN 0 0 100 0 1 500 1 0 200 11 1 LOGIC COMMON K1 OUT 10k +5V AD624 NC Figure 38. Gain Programmable Amplifier |
同様の部品番号 - AD624SD |
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同様の説明 - AD624SD |
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