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MAX2150ETI+ Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX2150ETI+ Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 16 page Detailed Description Internally, the MAX2150 includes a broadband I/Q modulator, internally matched broadband output driver amplifier, fine-resolution fractional-N frequency synthe- sizer, an LO buffer amplifier, and an on-chip low-noise crystal oscillator circuit. A simple 3-wire interface is provided for synthesizer programming and device configuration and control. Independent hardware and software power-down con- trol of the I/Q modulator, frequency synthesizer, and LO buffer amplifier is provided, as well as the ability to shut down the entire chip. I/Q Modulator The MAX2150 modulator is composed of a pair of matched double-balanced mixers, a broadband pas- sive LO quadrature generator, and a summing amplifi- er. The mixers accept differential I/Q baseband signals that directly modulate the internal 0 ° and 90° LO sig- nals applied to the I/Q mixers. An external LO source drives an internal LO quadrature generator that shifts the phase of the LO signal applied to the Q mixer by 90 ° relative to the LO signal applied to the I-channel mixer. The modulated output of the I/Q mixers is summed together, and the undesired sideband is sup- pressed. The I+, I-, Q+, and Q- input ports feature high-linearity buffer amplifiers with a typical -3dB bandwidth of 75MHz and accept differential input voltages up to 1VP-P. The ports require external biasing and have an input common-mode requirement of 1.6V. For single- ended operation, bypass the I and Q ports to ground. See the Typical Application Circuit for recommended component values. The broadband output driver amplifier is matched on chip across the entire operating frequency range and requires an output DC-blocking capacitor. For optimum performance, the output match can be improved with simple L-section and/or PI-section matching networks. Always ensure that DC blocking is provided, because internal bias voltages are present at this output. The modulator can be shut down with both hardware (pin 1) and software (TE bit). This mode is useful for quiet synthesizer programming or to mute the RF out- put signal. The hardware pin and software bits must be set to logic-1 to enable the modulator. If the hardware pin or software bit is set to logic-0, or if both are set to logic-0, the modulator is disabled. LO Buffer Amplifier The broadband buffer amplifier output is internally matched and requires a DC-blocking capacitor to iso- late on-chip bias voltages. Power-down of the LO buffer can be controlled by both BUFEN (pin 23), as well as BUFEN by software by setting the BUFEN (BE) bit through the 3-wire interface. The hardware pin and the software bit must be a logic-1 to enable the buffer. If the hardware or software bit is set to logic-0, the LO buffer is disabled. Frequency Synthesizer The MAX2150 features an internal 28-bit sigma-delta frequency synthesizer. This architecture enables the use of very high (30MHz) comparison frequencies, which significantly reduces the in-loop phase noise as a result of reduced division ratios. The high comparison frequency also allows significantly increased PLL bandwidths for very fast switching speed applications. Divider Programming The MAX2150 frequency programming is determined as follows. The overall division ratio (D) has an integer value (N), as well as a fractional component (F): D = N.F = N +F / 228 The N and F values are encoded as straight binary numbers. Determination of these values is illustrated by the following example: FLO = 1721.125MHz, FCOMP = 20MHz Then: D = 1721.125 / 20 = 86.05625 Therefore: N = 86 and F = 0.05625 x 228 = 15,099,494 Wideband I/Q Modulator with Sigma-Delta Fractional-N Synthesizer _______________________________________________________________________________________ 9 Pin Description (continued) PIN NAME FUNCTION 26, 27 I-, I+ Differential I-Channel Baseband Inputs to the Modulator. These pins connect directly to the bases of a differential pair and require an external common-mode bias voltage of 1.6V. 28 VCC_RF Supply Voltage Input for RF Circuits. Bypass as close to pin as possible. The bypass capacitor should not share ground vias with other branches. — Exposed pad Ground |
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