7.4.1 Internal LO Mode

When using internal LO mode, the integrated synthesizer is activated to generate the desired LO frequency. The OSCINP and OSCINM pins are used to provide a reference frequency to the PLL and are required to generate the internal state machine clock. The CP pin generates the phase detector output for use with an external loop filter. The filtered phase detector output is fed into the VTUNE pin to control the internal VCO, generating frequencies between 7.5 GHz and 15 GHz. The VCO output is divided down to close the loop into the phase detector. The VCO output may be fed directly into the I/Q generation circuitry.

The I/Q generation circuitry has two paths: a divide-by-2 path, and a polyphase filter path. Depending on the frequency of the LO, the I/Q generation circuitry used will differ. The divide-by-2 path requires the VCO frequency to be double that of the LO frequency. When the LO frequency is between 4 GHz and 7.5 GHz, the VCO can be programmed to between 8 GHz and 15 GHz, and the VCO output can be fed into the divide-by-2 path. When the LO frequency is greater than 7.5 GHz, the VCO can be programmed to between 7.5 GHz and 15 GHz, and the VCO output can be fed into the polyphase filter path.

In Internal LO mode, the LO pins may be used as outputs (refer to LO Interface as Output Port) for three separate signals internal to the device:

1. The VCO output may be fed directly to the LO pins.
2. The VCO may be divided by any possible combination using the channel divider, and the divided output may be fed to the LO pins. Refer to the datasheet of LMX2594 for more details.