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ADF4360-1 датащи(PDF) 10 Page - Analog Devices |
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ADF4360-1 датащи(HTML) 10 Page - Analog Devices |
10 / 20 page ADL5370 Rev. 0 | Page 10 of 20 THEORY OF OPERATION CIRCUIT DESCRIPTION Overview The ADL5370 can be divided into five circuit blocks: the local oscillator (LO) interface, the baseband voltage-to-current(V-to-I) converter, the mixers, the differential-to-single-ended (D-to-S) amplifier, 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 differential-to-single-ended amplifier, which provides a 50 Ω output interface. The bias cell generates reference currents for the V-to-I stage and the D-to-S amplifier. 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, 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 varies 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 ADL5370 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 amplifier. D-to-S Amplifier The output D-to-S amplifier consists of a totem pole output stage. The 50 Ω output impedance is established by an on-chip resistor. The D-to-S output is internally dc-biased and should be ac-coupled at its output (VOUT). 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 and a temperature independent current for the D-to-S output stage. |
Аналогичный номер детали - ADF4360-1 |
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Аналогичное описание - ADF4360-1 |
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