7.3.14.2.1 Automatic Ramping Example (Triangle Wave)
Suppose user wants to generate a sawtooth ramp that goes from 8 to 10 GHz in 2 ms (including calibration breaks) with a phase-detector frequency of 50 MHz. Divide this into segments of 50 MHz where the VCO ramps for 25 µs, then calibrates for 25 µs, for a total of 50 µs. There would therefore be 40 such segments which span over a 2-GHz range and would take 2 ms, including calibration time.
Table 18. Sawtooth Ramping Example
FIELD |
PROGRAMMING |
DESCRIPTION |
RAMP_EN |
1 = Enabled |
|
RAMP_MANUAL |
0 = Automatic ramping mode |
|
RAMP_TRIG_CAL |
0 = Disabled |
|
RAMP_THRESH |
16777216 (= 50-MHz ramp_thresh) |
50 MHz / 50 MHz × 224 = 16777216 |
RAMP_DLY |
0 = 1 clock cycle |
|
RAMPx_LEN |
50000 |
1000 µs × 50 MHz = 50000 |
RAMP0_INC |
13422 |
(2000 MHz) / (50 MHz) × 224 / 50000 = 13422 |
RAMP1_INC |
1073728402 |
(–2000 MHz) / (50 MHz) × 224 / 50000 = –13422
2’s complement = 230 – 13422 = 1073728402 |
RAMP0_NEXT |
1 = RAMP1 |
|
RAMP1_NEXT |
0 = RAMP0 |
|
RAMPx_NEXT_TRIG |
0 = Timeout counter |
|
RAMP_TRIG_x |
0 = Disabled |
|
RAMP0_RST |
1 = Enabled |
Not necessary, but good practice to reset. |
RAMP1_RST |
0 = Disabled |
Do not reset this, or ramp does not work. |
RAMP_BURST_COUNT |
0 |
|
RAMP_BURST_TRIG |
0 = Ramp Transition |
|
NOTE
To calculate ramp_scale_count and ramp_dly_cnt, remember that the desired calibration time is 25 µs.