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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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ISL55211IRTZ-EVAL1Z Fiches technique(PDF) 11 Page - Intersil Corporation |
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ISL55211IRTZ-EVAL1Z Fiches technique(HTML) 11 Page - Intersil Corporation |
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11 / 20 page  ISL55211 11 FN7868.0 June 21, 2011 Working with a transformer coupled input as shown in Figure 29, or with two DC blocking caps from a differential source, means the output common mode voltage set by either the default internal VCM setting, or a voltage applied to the VCM control pin, will also appear as the input common mode voltage. This provides a very easy way to control the ISL55211 I/O common mode operating voltages for an AC-coupled signal path. The internal common mode loop holds the output pins to VCM and, since there is no DC path for an ICM current back towards the input in Figure 29, that VCM setting will also appear as the input common mode voltage. It is useful, for this reason, to leave any input transformer secondary centertap unconnected. The internally set VCM voltage is referenced from the negative supply pin. With a single 3.3V supply, it is very close to 1.2V but will change with total supply voltage across the device as shown in Figure 27. Most of the characterization curves starting with Figure 29 then get different gains by changing the connections to the two pairs of input RG connections, as shown on the pin configuration drawing on page 2. Two input turns ratios are intended for Test Circuit 1; either a 1:1.4 turns ratio (ohms ratio of 2) or a 1:2 turns ratio (ohm ratio of 4). The specific transformers shown in Figure 29 are representative of broadband RF transformers but alternate devices and manufacturers of these turns ratio devices are certainly applicable. The output side of this test circuit presents a differential 200Ω load while converting the differential to single-ended through a resistive attenuator and a 1:1 transformer. This inserts approximately a 17dB insertion loss that is removed to report the characteristic curves. For load tests below the 200Ω shown in Figure 29, a simple added shunt resistor is placed across the output pins. For loads > 200Ω, the series and shunt load R's are adjusted to show that total load (including the 50Ω measurement load reflected through the 1:1 output measurement port transformer) and provide an apparent 50Ω differential source to that transformer. This output side transformer is for measurement purposes only and is not necessary for final applications circuits. There are output interface designs that do benefit from a transformer as part of the signal path as shown in Figure 1. In that case, the 1:1:4 output side transformer becomes part of a filter design and recovers the filter insertion loss from the amplifier output pins to the ADC inputs. Where just the amplifier is tested, a 4-port network analyzer is used and the very simple test circuit of Figure 30 is implemented. This is used to measure the differential S21 curves vs gain of Figure 17 and as a simulation circuit for the differential output impedance vs gain of Figure 18. Changing the gain is a simple matter of adjusting the connections to the four input RG connections resistors, as shown in Table 1. This circuit depends on the two AC-coupled source 50 Ω of the 4 port network analyzer and presents an AC-coupled differential 100 Ω load to the amplifier as the input impedance of the remaining two ports of the network analyzer. Using this measurement allows the small single bandwidth of just the ISL55211 to be exposed. Many of the other measurements are using I/O transformers that are limiting the apparent bandwidth to a reduced level. Figure 17 shows the 3 normalized differential S21 curves for the possible internal gains of 9dB, 14dB and 15dB. The small signal bandwidth is remaining nearly constant at 1.4GHz due to the internal capacitive feedback network. The closed loop differential output impedance of Figure 18 is simulated using Figure 30 in ADS. This shows a relatively low output impedance (< 1Ω through 100MHz) constant with signal gain setting. Typical FDA outputs show a closed loop output impedance that increases with signal gain setting. The ISL55211 holds a more constant response due to internal design elements unique to this device. Common mode output measurements are made using the circuit in Figure 31. Here, the outputs are summed together through two 100Ω resistors (still a 200Ω differential load) to a center point where the average, or common mode, output voltage may be sensed. This is coupled through a 1µF DC blocking capacitor and measured using 50Ω test equipment. The common mode source impedance for this circuit is the parallel combination of the 2-100Ω elements, or 50Ω. Figure 19 uses this circuit to measure the small and large signal response from the VCM control pin to the output common mode. This pin includes an internal 50pF capacitor on the default bias network (to filter supply noise when there is no connection to this pin), which bandlimits the response to approximately 30MHz. This is far lower than the actual bandwidth of the common mode loop. Figure 20 uses this output FIGURE 29. TEST CIRCUIT 1 50 1µF 1:1.4 1µF 1µF 85 ISL55211 +3.3V + - Vi 35 35 ADT2- 1T or ADT4- 1Wt 0.1µF VCM 500 500 35mA 115mW 1:1 ADT1- 1WT 50 1µF Vm VO RG RG PD 0.2pF 0.2pF RT 200 85 10k FIGURE 30. TEST CIRCUIT 2 4-PORT S-PARAMETER MEASUREMENTS ISL55211 +3.3V + - 50 50 VCM RF RF 50 1/2 of a 4-port S-parameter 1/2 of a 4-port S-parameter 10k PD RG RG RT 50 |
Numéro de pièce similaire - ISL55211IRTZ-EVAL1Z |
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Description similaire - ISL55211IRTZ-EVAL1Z |
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