FREQUENCY_SYNTHESIZER_

Published:2009/7/13 23:55:00 Author:May | From:SeekIC

The MAX038 and four other ICs can form a crystal-controlled, digitally programmed frequency synthesizer that produces accurate sine, square, or triangle waves in 1-kHz increments over the range 8 kHz to 16.383 MHz. Each of the 14 manual switches (when open) makes the listed contribution to output frequency: Opening only S0, S1, and S8, for example, produces an output of 259 kHz. The switches generate a 14-bit digital word that is applied in parallel to the D/A converter (IC2) and a ÷N circuit in IC1. IC1 also includes a crystal-controlled oscillator and high-speed phase detector, which form a phase-locked loop with the voltage-controlled oscillator in IC5. The DAC and dual op amp (IC4) produce a 2- to 750-μA current that forces a coarse setting of the IC5 output frequency-sufficient to bring it within capture range of the PLL. This loop, in which the phase detector in IC1 compares IC5's SYNC output with the crystal-oscillator frequency divided by N, produces differential-phase information at PDV and PDR. IC3 then filters and converts this information to a ±2.5-V single-ended signal, which, when summed with an offset and applied to FADJ, forces the signal output frequency to the exact value set by the switches.



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