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OPA4658 Fiches technique(PDF) 11 Page - Burr-Brown (TI) |
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OPA4658 Fiches technique(HTML) 11 Page - Burr-Brown (TI) |
11 / 14 page 11 ® OPA4658 –50 –60 –70 –80 –90 –100 Load Resistance ( Ω) 10 100 1k 2f O 3f O G = +2 The third-order intercept is an important parameter for many RF amplifier applications. Figure 6 shows the OPA4658’s two tone, third-order intercept vs frequency. This curve is particularly useful for determining the magnitude of the third harmonic as a function of frequency, load resistance, and gain. For example, assume that the application requires the OPA4658 to operate in a gain of +2V/V and drive 2Vp-p into 100 Ω at a frequency of 10MHz. Referring to Figure 6 we find that the intercept point is +38dBm. The magnitude of the third harmonic can now be easily calcu- lated from the expression: Third Harmonic (dBc) = 2(OPI3P – P O) where OPI3P = third-order output intercept, dBm P O = output level, dBm For this case OPI3P = 38dBm, PO = 7dBm, and the third Harmonic = 2(38 – 7) = 62dB below the fundamental. The OPA4658’s low distortion makes the device an excellent choice for a variety of RF signal processing applications. CROSSTALK Crosstalk is the undesired result of the signal of one channel mixing with and reproducing itself in the output of another channel or channels. Crosstalk is inclined to occur in most multichannel integrated circuits. In quad devices, the effect of crosstalk is measured by driving three channels and observing the output of the undriven channel over various frequencies. The magnitude of this effect is referenced in terms of channel- to-channel isolation and expressed in decibels. Input referred points to the fact that there is a direct correlation between gain and crosstalk, therefore at increased gain, crosstalk also in- creases by a factor equal to that of the gain. Figure 7 illustrates the measured effect of crosstalk in the OPA4658U. FIGURE 5. 5MHz Harmonic Distortion vs Load Resistance. FIGURE 6. Third Order Intercept Point vs Frequency. 70 60 50 40 30 20 100k 1M 10M 100M Frequency (Hz) G = +2 (G = +2, R L = 100Ω, RFB = 402Ω) FIGURE 8. Configuration for Testing Differential Gain/Phase. OPA4658 75 Ω 75 Ω 402 Ω 402 Ω 75 Ω 75 Ω TEK TSG 130A TEK VM700A 1/4 DIFFERENTIAL GAIN AND PHASE Differential Gain (DG) and Differential Phase (DP) are criti- cal specifications for video applications. DG is defined as the percent change in closed-loop gain over a specified change in output voltage level. DP is defined as the change in degrees of the closed-loop phase over the same output voltage change. Both DG and DP are specified at the NTSC sub-carrier frequency of 3.58MHz and the PAL subcarrier of 4.43MHz. All NTSC measurements were performed using a Tektronix model VM700A Video Measurement Set. DG and DP of the OPA4658 were measured with the amplifier in a gain of +2V/V with 75 Ω input impedance and the output back-terminated in 75 Ω. The input signal selected from the generator was a 0V to 1.4V modulated ramp with sync pulse. With these conditions the test circuit shown in Figure 8 delivered a 100IRE modulated ramp to the 75 Ω input of the video analyzer. The signal averaging feature of the analyzer FIGURE 7. Channel-to-Channel Isolation (three active channels). Frequency (Hz) 10 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 1M 10M 100M G = +2 |
Numéro de pièce similaire - OPA4658 |
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Description similaire - OPA4658 |
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