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AN1777 Datasheet(PDF) 10 Page - NXP Semiconductors |
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AN1777 Datasheet(HTML) 10 Page - NXP Semiconductors |
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10 / 31 page  Philips Semiconductors Application note AN1777 Low voltage front-end circuits: SA601, SA620 1995 Aug 10 10 is placed in parallel with an inductor, it has no effect on the Q-point, but does influence the slope of the AC load line as Slope = -1 R C ) -1 R LOAD . The capacitor CS functions not only as a DC blocking capacitor, but is also chosen such that the impedance presented by the combination of L, RC and CS is equal to RLOAD for optimum power transfer. The analysis is done in the following manner. First, note that inductor L is connected to VCC which is an effective AC ground. So, L can be redrawn to ground. Next, RC and CS are converted to their parallel equivalent values as shown in Figure 17. The resulting parallel LCR circuit is shown in Figure 18. At resonance, the parallel L, CP combination will be an effective open circuit leaving only RP. RP is then simply chosen to be equal to RLOAD. VCC CS AB RC RLOAD DC BLOCKING CAPS L CB SR01277 Figure 16. Flexible Matching Circuit CP RP CS RC Q + X S R C R P + (Q 2 ) 1) R C X P + R P Q P C P + 1 2 pFX P GOAL: Convert series RC and CS into a parallel combination RP and CP SR00014 Figure 17. Converting from Series to Parallel Configuration CP RP L GOAL: Find LC and CP such that RP looks like RLOAD value @ the resonant frequency SR01278 Figure 18. Converting from Series to Parallel Configuration ii IF IF RF RF BASIC MIXER SIMPLE MODEL IF IF SR01279 Figure 19. Circuit Model of Differential Open-Collector Output RF VCC C 2L C 14 13 SR01280 Figure 20. External current-combiner Circuit 2L i i CC SR01281 Figure 21. Ideal AC Equivalent Circuit VII. SA601 MIXER [6] The SA601 mixer is intended for operation with an external VCO and employs a differential output structure. The current wireless markets demand front-end solutions with low power, and high gain. The differential output offers higher gain than the conventional single-ended open-collector output without an increase in supply current. An equivalent model can be seen in Figure 19. A characteristic of the differential output is that the two output currents are 180 ° out of phase. This is why the mixer output is labeled IF and IF. The current-combiner circuit shown in Figure 20 consists of two capacitors and one inductor. The purpose of the current-combiner is to combine the currents such that they are in phase with one another. By aligning the currents in phase with one another, the output will have a larger AC output swing due to the increased signal current. Figure 21 shows the ideal AC equivalent model. In the ideal case, it is assumed that all component Q’s are high enough to be neglected and the output impedances of the current sources are also high enough to be neglected. By source transformation, the parallel capacitor and current source can be converted to a voltage source and a source capacitor. The inductor, 2L, can be split into two inductors where L becomes the new value (See Step 2 in Figure 22). Since two inductors of equal value in series will be twice that |
Similar Part No. - AN1777_15 |
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Similar Description - AN1777_15 |
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