LMX2582 PLL |
Key Features:
- Wideband PLLatinum RF Synthesizer LMX2582 (5.5GHz) or LMX2592 (9.8GHz)
- 120MHz clock locked to internal OCXO reference
- automatic switching between internal / external 10MHz reference
- RF output A used, Output level ~17dBm / 300MHz, 7dBm / 5GHz
- up to 16 possible software defined frequencies, Arduino IDE compatible
- external control via uWire interface or other SPI controller
Below, I present a PLL based on the LMX2582, designed as a signal source for various experimental applications. LMX2582 IC was selected due to its versatile output divider, capable of dividing the internal VCO by factors such as 2, 3, 4, 6, 8, and more. This functionality is particularly valuable for applications requiring precise submultiple frequencies. The software is easy to customize, supporting up to 16 predefined frequencies that can be selected using a BCD switch. I have utilized a BCD switch with only 10 positions, where position 0 disables the internal controller to enable external programming via uWire or SPI. It is fully compatible with the USB2ANY interface and TICS Pro software from Texas Instruments. In the next example, I have programmed only 4 frequencies (310.7 MHz and submultiples).
The controller's software is straightforward to modify, and the 46 registers can be easily calculated offline using TICS Pro, screenshots >>1<<, >>2<<, >>3<<.
I didn't focus on achieving a high output level at high frequencies. Component's values related to the LMX2582 output stage and MMIC were selected for relatively low frequencies.
The mechanism for automatically selecting the reference frequency (internal or external) may seem quite complex, it is implemented using an inverter gate as an amplifier, a few logic gates for switching, and a monostable that detects the presence of external reference. Entire block can be removed if external 10 MHz synchronization is not required. It is similar to the one used in the MARCONI 2440 frequency counter, but I replaced the IC SN75107, which requires a negative supply voltage. The 74HC04 inverter gate used as an amplifier ensures a minimum input signal of -25dBm / 10MHz.
As the VCXO "clock" source, I selected the VXO-P9-3PE50-15 120MHz oscillator, purchased from eBay at a much more affordable price compared to Mouser. These oscillators from QuartzCom are simple Collpits overtone oscillators with a bipolar transistor and the associated varicap diode. The same applies to those manufactured by Crysted (CVHD series) or Abracon (ABLNO series). Some of them also include a logic gate for LVPECL or CMOS output.
Other oscillators may also be utilized, as the tuning frequency of the ADF4001 can be easily adjusted. The register values are calculated using the ADI PLL Int-N software from Analog Devices.
I have not yet tested LMX2592, but it is pin-to-pin compatible with the LMX2582, same core.
LMX2582 PLL Schematic vers.1
LMX2582 PCB vers.1a (Gerber)
PCB top view
PCB bottom view
Simplified schematic of reference switch
LMX2582 vers.1 sketch - free to be modified
Attiny84 firmware vers.1 (hex)
Attiny84 fuse bits
Attiny84 IDE board
>>Link to ATTinyCore 2.0<<
