wide tuning range sine wave generation up to RF

Hi all,


I'm curious how RF instruments manufacturers design wide tuning-range sine-wave generators. For instance, suppose I need to generate a sine wave from 1 MHz to 5 GHz. How is it normally done? My thinking:

PLL - generally only generates sine wave at the oscillation frequency. Lower ranges are square.
DAC - limited by sampling rate. Nowadays its possible to generate up to the GHz range, but very expensive.

The only thing alternative I see is to split the frequency range into several sub-ranges. You would then need to filter each sub-range, and combine them later. Essentially a kind of tunable filter.

Any thoughts?


thanks,
Aaron

Normally it would be a VCO offset by the fmax performed by a voltage controlled cavity resonator using lookup table corrected values for linearity.

1) A large number of smart calibrated digital / voltage controlled filters are required. (DVCF) as follows;
a) intermodulation tracking notch filter
b) tracking bandpass filter
c) all-pass phase shift correction filter

2) digitally biased power amps.
3) Injection Locked oscillators
4) Electrically controlled bandstop filters.
5) hi-res ADC
6) Log RMS power detector

Thanks for the reply.

I didn't quite understand some of it. So you're saying that you take two VCOs and mix them together (one of which is a voltage controlled cavity resonator)? What did you mean by "offset by the fmax"? In my example (1 MHz to 5 GHz), can you give some numbers? I can imagine that you could mix together two oscillators, one tunable from 5 GHz to 10 GHz, and the other fixed at 4.999GHz.

Why do you need an intermodulation tracking filter? I see only the two tones which you intend to mix anyway. Are you referring to the unwanted side-bands of the mixing of the two VCOs? In the example numbers above, the unwanted sidebands should be easily filtered with a LPF.

How about the phase-shift correction filter? Does it matter for a sine wave?

I don't understand why you would need injection-locked oscillators, but I assume you're referring to a different possible architecture.

Do you know of any good documents to read about this?


thanks,
Aaron

Classical RF generators don't use tunable filters, just the basic means:
- a synthesizer generator, e.g. 0.5 - 1 GHz
- frequency multipliers and dividers to extend the range
- switchable low pass filters to select the fundamental wave
- a downmixer with respective filters to cover the low frequency range

Review manuals of industry standard generators for detail insights.