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ADL5372 Arkusz danych(PDF) 11 Page - Analog Devices |
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ADL5372 Arkusz danych(HTML) 11 Page - Analog Devices |
11 / 24 page ADL5372 Rev. 0 | Page 11 of 24 THEORY OF OPERATION CIRCUIT DESCRIPTION Overview The ADL5372 can be divided into five circuit blocks: the LO interface, the baseband voltage-to-current (V-to-I) converter, the mixers, the differential-to-single-ended (D-to-S) stage, and the bias circuit. A detailed block diagram of the device is shown in Figure 24. PHASE SPLITTER OUT LOIP LOIN IBBP IBBN QBBP QBBN Σ Figure 24. Block Diagram The LO interface generates two LO signals in quadrature. These signals are used to drive the mixers. The I and Q baseband input signals are converted to currents by the V-to-I stages, which then drive the two mixers. The outputs of these mixers combine to feed the output balun, which provides a single-ended output. The bias cell generates reference currents for the V-to-I stage. LO Interface The LO interface consists of a polyphase quadrature splitter followed by a limiting amplifier. The LO input impedance is set by the polyphase. The LO can be driven either single-ended or differentially. When driven single-ended, the LOIN pin should be ac grounded via a capacitor. Each quadrature LO signal then passes through a limiting amplifier that provides the mixer with a limited drive signal. V-to-I Converter The differential baseband inputs (QBBP, QBBN, IBBN, and IBBP) consist of the bases of PNP transistors, which present a high impedance. The voltages applied to these pins drive the V-to-I stage that converts baseband voltages into currents. The differential output currents of the V-to-I stages feed each of their respective Gilbert-cell mixers. The dc common-mode voltage at the baseband inputs sets the currents in the two mixer cores. Varying the baseband common-mode voltage influences the current in the mixer and affects overall modulator performance. The recommended dc voltage for the baseband common-mode voltage is 500 mV dc. Mixers The ADL5372 has two double-balanced mixers: one for the in-phase channel (I-channel) and one for the quadrature channel (Q-channel). Both mixers are based on the Gilbert-cell design of four cross-connected transistors. The output currents from the two mixers sum together into a load. The signal developed across this load is used to drive the D-to-S stage. D-to-S Stage The output D-to-S stage consists of an on-chip balun that converts the differential signal to a single-ended signal. The balun presents high impedance to the output (VOUT). Hence, a matching network may be needed at the output for optimal power transfer. Bias Circuit An on-chip band gap reference circuit is used to generate a proportional-to-absolute temperature (PTAT) reference current for the V-to-I stage. |
Podobny numer części - ADL5372_15 |
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Podobny opis - ADL5372_15 |
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