Hi!,

We are evaluating TI components for one block: Chirp generator

Architecture context: Our RF front-end uses a heterodyne approach. A swept LO at X-Band (~12 GHz) drives two image-reject mixers (TX and RX), each with an internal ×2 frequency multiplier to produce a 24.0 - 24.25 GHz FMCW chirp (BW = 250 MHz). The chirp generator must therefore sweep 125 MHz at X-Band (BW_RF = 250 MHz after x2), autonomously, triggered by an external signal from the LMK04828.

Key requirement that constrains the solution: the chirp generator must execute a linear frequency ramp (without SPI reprogramming during the chirp). Each ramp is 4.0 us. At 31.25 MHz/us slope, the frequency must step from 11.875 GHz to 12.000 GHz in a controlled, linear, hardware-driven fashion. A conventional PLL/synthesizer reprogrammed over SPI might not meet this requirement due to SPI latency and PLL settling time.

Full requirements:

Output frequency range: 11.875 - 12.125 GHz BW_X = 125 MHz -> BW_RF = 250 MHz after x2
Chirp waveform: Linear sawtooth
Slope at output: 31.25 MHz/us slope_RF = 62.5 MHz/us after x2
Chirp duration: T_chirp = 4.0 us 1480 ADC samples @ 370 MSPS
Chirp period: T_ramp = 9.0 µs T_ON = 4.0 us + T_OFF = ~5.0 us
External digital trigger from LMK04828
Output power at 12 GHz ≥ +6 dBm into 50 Ω 2x mixers simultaneously (each 2-9 dBm); gain block acceptable
Reference input 100 MHz, 20 fs (from LMK04828 CLKOUT) 
Programming SPI, one-time boot config Host: J784S4 R5F core

Current evaluation: We would strongly prefer a TI-native solution for ecosystem coherence with J784S4 + LMK04828.

We have reviewed the LMX2820 datasheet. While its phase noise performance is excellent (36 fs at 6 GHz), the LMX2820 is a fixed-frequency synthesizer with no integrated frequency ramp generator, it requires SPI reprogramming to change frequency, which might be incompatible with a 4.0 us chirp. The LMX2492 supports frequency ramping but is limited to ~9.8 GHz output (does not reach 12 GHz).

Our open questions are therefore:

Q1. Does TI have any wideband synthesizer or dedicated chirp generator with an integrated hardware frequency ramp generator (analogous to a Digital Ramp Generator / FCW accumulator) that can reach 12 GHz output?

Q2. If no single-chip solution exists, does TI have a DDS product capable of generating a linear ramp at ~94 MHz (step size ~0.244 MHz/µs, 4.0 us duration, triggered externally), suitable for use as reference to an integer-N PLL (x128 -> 12 GHz via LMX2820)?

Q3. If TI does not have a direct solution (neither integrated ramp synthesizer nor DDS at this frequency), what is TI's recommended architecture for FMCW chirp generation at 12 GHz using TI components, compatible with the LMK04828 + J784S4 ecosystem already committed?

Q4. Is there a TI application note or reference design for FMCW radar chirp generation at 12-24 GHz with any combination of TI components?

Thank you for your time.