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ISL55211 Folha de dados(PDF) 10 Page - Intersil Corporation |
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ISL55211 Folha de dados(HTML) 10 Page - Intersil Corporation |
10 / 20 page ISL55211 10 FN7868.0 June 21, 2011 Applications Basic Operation The ISL55211 is a very wideband, voltage feedback based, differential amplifier including an output common mode control loop and optional power shutdown feature. Intended for very low distortion differential signal driving, this internally fixed gain device provides 3 possible gain settings by simply picking the input side connections as shown in Table 1. Including internal compensation, the ISL55211 holds a constant bandwidth over gain settings. Most applications are intended for AC-coupled I/O using a single 3.3V supply and an input transformer. The internal resistor values have been scaled up slightly to require an external termination element along with the two internal resistors where a 50Ω differential input match is desired. This does increase the output noise slightly but narrows up the input VSWR tolerance and lowers the added loading of the feedback resistors improving SFDR. Where DC-coupled differential I/O operation is desired, the ISL55211 can be connected directly to the source as long as the internal input common mode range limits are observed (1.1V to 1.7V for a 3.3V single supply operation). For a DC-coupled, single to differential requirement, consider the ISL55210. This device is an external resistor version of the ISL55211 where the flexibility in the external resistors will enable single to differential operation. For a ground referenced input signal, this will require a negative supply when using the ISL55210. Most applications behave as a differential inverting op amp design. There is therefore an input gain resistor on each side of the inputs that must be driven. The 3 possible connections to the two pairs of input pins will give a 100Ω, 125Ω, or 250Ω input resistor on each side. Combined with the two input turns ratio's shown in Table 1, gives a 9dB to 20dB operating gain range in approximately 3dB steps. The device can be powered down to < 400µA supply current using the optional disable pin. To operate normally, this pin should be asserted high using a simple logic gate to +VCC or tied high through a 10kΩ resistor to +VCC. When disabled, the power dissipation drops to < 1mW but, due to the inverting op amp type architecture, the input signal will feed-forward through the feedback and gain resistors giving limited isolation. Application and Characterization Circuits Test Circuit 1 of Figure 29 forms a starting point for many of the characterization curves for the ISL55211. Since most lab sources and measurement devices are single-ended, this circuit converts to differential at the input through a wideband transformer and would also be a typical application circuit coming from a single-ended source. Assuming the source is a 50Ω impedance, the internal RG resistors and external RT are set to provide both the input termination and the gain. Since the inverting summing nodes act as virtual ground points for AC signal analysis, the total termination impedance across the input transformer secondary will be (2*RG)||RT. Setting this equal to n2*RS will give a matched input impedance inside the bandwidth of the transformer (where "n" is the turns ratio). The amplifier gain is fixed by the selected input RG element and the internal 500Ω feedback resistors. While the ISL55211 is internally a Voltage Feedback Design (VFA) to give the lowest possible noise, internal compensation caps hold the bandwidth over gain setting approximately constant at 1.4GHz. For wider small signal bandwidth at lower gains, consider the ISL55210, which provides >2.2GHz at a gain of 12dB. FIGURE 27. DEFAULT VCM AND MAX VOPP vs SUPPLY VOLTAGE FIGURE 28. SUPPLY CURRENT vs SUPPLY VOLTAGE Typical Performance Curves V s+ = 3.3V, TA ≈ +25°C, unless otherwise noted. (Continued) 1 2 3 4 5 6 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5 SUPPLY VOLTAGE (V) INTERNALLY SET VCM MAXIMUM DIFFERENTIAL VP-P OUTPUT USING DEFAULT VCM TEST CIRCUIT 1 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5 SINGLE SUPPLY VOLTAGE (V) TA = +25°C TA = -40°C TA = +85°C TEST CIRCUIT 1 |
Nº de peça semelhante - ISL55211 |
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Descrição semelhante - ISL55211 |
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