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CLC522AJE Datasheet(PDF) 4 Page - National Semiconductor (TI) |
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CLC522AJE Datasheet(HTML) 4 Page - National Semiconductor (TI) |
4 / 8 page Theory of Operation The CLC522 is a linear wideband variable-gain amplifier as illustrated in Fig 1. A voltage input signal may be applied differentially between the two inputs (+Vin, -Vin), or single-endedly by grounding one of the unused inputs. The CLC522 input buffers convert the input voltage to a current (IRg) that is a function of the differential input voltage (Vinput =+Vin - -Vin) and the value of the gain- setting resistor (Rg). This current (IRg) is then mirrored to a gain stage with a current gain of 1.85. The voltage- controlled two-quadrant multiplier attenuates this current which is then converted to a voltage via the output amplifier. This output amplifier is a current-feedback op amp configured as a transimpedance amplifier. It's tran- simpedance gain is the feedback resistor (Rf). The input signal, output, and gain control are all voltages. The output voltage can easily be calculated as seen in Eq. 1. Eq. 1 Fig. 1 Phase Negative Sync Phase Positive Sync Gain Positive Sync Gain Negative Sync 4.43 MHz Avmax = +10 Vg = 1.0V Num ber of 150 Ω Loads Differential Gain and Phase 1234 .25 .20 .15 .10 .05 0 .25 .20 .15 .10 .05 0 50MHz 20MHz 10MHz 5MHz -4 -2 02 4 6 8 10 Output Power (Pout, dBm) -35 -40 -45 -50 -55 -60 -65 -70 -75 -80 -85 2nd Harmonic Distortion vs. Pout 1.1V 50 Ω Po 1k Ω 50 Ω 50 Ω 50 Ω 20 Ω 182 Ω Rf Vg 522 50MHz 20MHz 10MHz 5MHz -4 -2 0 2 4 6 8 10 Output Power (Pout, dBm) -35 -40 -45 -50 -55 -60 -65 -70 -75 -80 -85 3rd Harmonic Distortion vs. Pout 1.1V 50 Ω 50 Ω 1k Ω 50 Ω 50 Ω 20 Ω 182 Ω Rf Vg 522 Po Input Limited Rf = 900 Ω Output Limited Rf = 1.4k Ω 0 100 Frequency (MHz) 20 19 18 17 16 15 14 13 12 11 10 -1dB Compression at Maximum Gain Po Pi Rg Rf 50 Ω 50 Ω 50 Ω 20 Ω 50 Ω 522 CLC522 Typical Performance (TA=+25°C, Vcc=±5V, Av=+10, Vg=1.1V, RL=100Ω; unless noted) Phase, Vg = 0.0V Phase, Vg = 1.0V Gain, Vg = 0.0V Gain, Vg = 1.0V 4.43 MHz Positive Sync Avmax = +2 Number of 150 Ω Loads Differential Gain and Phase 1234 .10 .08 .06 .04 .02 0 .10 .08 .06 .04 .02 0 0 10 20 3040 50 6070 80 90 100 Maximum Gain Setting, AVmax (V/V) 100 10 1 Input Referred Voltage Noise vs AVmax VI V R out R g f g =∗ ∗ + ∗ 185 1 2 . sin . ce I V R A R R V R input g v f g g g = =∗ ∗ + 185 1 2 Eq. 2 The gain of the CLC522 is therefore a function of three external variables; Rg, Rf and Vg as expressed in Eq. 2. The gain-control voltage (Vg) has a ideal input range of -1V ≤Vg≤+1V. At Vg=+1V, the gain of the CLC522 is at its maximum as expressed in Eq. 3. A R R V f g max . = 185 Eq. 3 Notice also that Eq. 3 holds for both differential and single-ended operation. Choosing Rf and Rg Rg is calculated from Eq.4. V inputmax is the maximum peak R V I g input Rg = max max Eq. 4 input voltage (Vpk) determined by the application. IRg max is the maximum allowable current through Rg and is typically 1.8mA. Once AVmax is determined from the minimum input and desired output voltages, Rf is then determined using Eq. 5. These values of Rf and Rg are RR A fg V =∗ ∗ 1 185 . max Eq. 5 the minimum possible values that meet the input voltage and maximum gain constraints. Scaling the resistor values will decrease bandwidth and improve stability. Application Discussion http://www.national.com 4 |
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