Dual PLL Frequency Synthesizers Include DACs & Multipliers

A trio of dual phase-locked-loop (PLL) frequency synthesizers is said to be the first such devices to include two D/A converters and a voltage multiplier on a single chip. The devices are said to significantly simplify the design of local oscillators in receivers or carrier oscillators for transmitters. The dual DACs permit precision trimming of crystal frequencies and permit the use of lower-cost crystals. The MC145181, MC145225 and MC145230 also offer a smaller footprint by eliminating several external components.All three operate with a single 1.8V supply, which makes them compatible with 1.8V microcontrollers in applications powered by smaller two-cell battery packs. Each supports two independent loops with a single input reference. Phase noise reduction circuitry has been designed into each chip. The MC145181 operates at frequencies up to 550 MHz on the main loop and up to 60 MHz on the secondary loop. The MC145220 is capable of direct usage up to 1.2 GHz on the main loop and up to 550 MHz on the secondary loop, while the MC145230 operates to 2.2 GHz on the main loop and 550 MHz on the secondary loop. The MC145181 and MC145225 have minimum main-loop operating frequencies of 100 MHz and the MC145230 has a 500-MHz main-loop minimum frequency.The chips all offer two 8-bit DACs, which allow adjustment of oscillators in portable equipment to align with the base station's pilot frequency. The DACs can also be used to adjust RF power amplifier output.