The direct modulation method used in the transmission system is a way of applying frequency modulation to the PLL using inputs from a modulation circuit. With frequency modulation method, the configuration can be simplified by modulating the carrier wave directly without a Mixer.
These PLL Synthesizers are designed to allow for frequency modulation. The AK1590 is a PLL Synthesizer IC, the AK1574 is a VCO built-in IC, and the AK2400/AK2401A is an integrated device. These ICs can perform frequency modulation using the offset frequency adjustment function of the built-in ΔΣ Fractional-N PLL Synthesizer.
Transmitter circuit downsizing using direct modulation method
Circuit configuration example
Conventional transmitter circuit configuration
As shown in Figure 1, a digital signal is placed on a carrier wave using a Mixer.
Direct modulation circuit configuration
As shown in Figure 2, a transmitter circuit can be configured by modulating directly to a VCO without the Mixer.
A direct modulation circuit can be configured as shown in Figure 3 by using the AK1574 that is a IC with built-in VCO.
A direct modulation circuit can be configured as shown in Figure 4 by using VCO and the AK2401A that is direct conversion IC.
The AK1574 achieves the following performance with FSK error of 1 % or less.
Evaluation boards and application notes are available for easy evaluation.
Contact us if you wish to have a sample or evaluation board.