Voltage-controlled oscillator (VCO)

01

Match the band, tuning voltage and sensitivity

Mini-Circuits' ROS-150+ data sheet describes an octave-band VCO covering 75–150 MHz, tuned by 1–18 V with tuning sensitivity of 4.0–6.8 MHz/V, output power +9.5 dBm typical into 50 ohms, harmonics −23 dBc typical (−16 dBc maximum), and a 12 V supply at up to 20 mA, with a 3 dB modulation bandwidth of 0.1 MHz; it is aimed at test instrument signal generators, communications and VHF. [1]

Its ROS-800-719+ data sheet describes a VCO for PLL ICs with 5 V tuning: 797–806 MHz, tuning voltage 0.5–5 V, typical sensitivity 7 MHz/V, tuning port capacitance 20 pF, 3 dB modulation bandwidth 115 MHz, output −0.5 dBm, and a 5 V supply at up to 35 mA; its absolute maximum tuning voltage is 7 V. [2]

Editorial note: check that the VCO covers your band at the end points of your loop's charge-pump or op-amp tuning voltage, including over temperature, and that its tuning sensitivity suits your loop filter design.

A wide-band microwave VCO trades sensitivity for coverage. Synergy Microwave's DCO100200-5 (Rev. B, 2014) is a 0.3 × 0.3 in surface-mount VCO covering 1,000–2,000 MHz with a planar resonator, tuned from 0.5 V (1,000 MHz max) to 24 V (2,000 MHz min), with guaranteed points such as at least 1,250 MHz at 8 V and 1,650 MHz at 15 V. It lists tuning sensitivity of 30–70 MHz/V, tuning-port capacitance of 82 pF, a +5 V supply at 36 mA maximum, output of +1 dBm minimum, harmonic suppression of 12 dB typical, pulling of 5 MHz into a 1.75:1 VSWR, pushing of 5 MHz/V, and −40 to +85 °C operation. [3]

Give the supplier the frequency band, available tuning voltage range, required tuning sensitivity range, phase noise limits at each offset, output power and load, harmonic and spurious limits, supply voltage and current budget, pushing and pulling limits, operating temperature range, package and footprint, and whether the VCO will be used open loop or in a PLL.

02

Check phase noise, harmonics, pushing, pulling and drift

The ROS-150+ lists single-sideband phase noise of −80, −103, −127 and −144 dBc/Hz at 1 kHz, 10 kHz, 100 kHz and 1 MHz offsets, pulling of 0.8 MHz peak to peak into a 12 dB return loss load and pushing of 0.3 MHz/V. [1] The ROS-800-719+ lists −93, −118, −140 and −162 dBc/Hz at 1, 10, 100 and 1000 kHz, non-harmonic spurious of −90 dBc, harmonics of −24 dBc typical (−18 maximum), pulling of 0.2 MHz and pushing of 0.2 MHz/V. Both operate from −55°C to 85°C. [2] [1]

The ROS-150+ performance table shows how frequency moves with temperature: at 5 V tuning it gives 91.20 MHz at −55°C, 88.51 MHz at +25°C and 83.97 MHz at +85°C. [1]

The DCO100200-5 lists typical phase noise of −95 dBc/Hz at 10 kHz and −117 dBc/Hz at 100 kHz offset. [3]

Editorial calculation: that is a change of about 7.2 MHz (91.20 − 83.97) across −55°C to +85°C at fixed tuning voltage, so the tuning range must leave margin for temperature as well as part-to-part spread. [1]

Editorial calculation: with 30–70 MHz/V sensitivity, 1 mV of noise on the tuning line moves the Synergy VCO by 30–70 kHz, against about 4–7 kHz for the 75–150 MHz ROS-150+ at 4.0–6.8 MHz/V; wide-band VCOs need a quieter tuning voltage and loop filter. [3] [1]

03

See the bandwidth–phase noise trade-off in one product family

Crystek's CVCO55 family of 0.50 in square surface-mount VCOs spans 38 MHz to 6,900 MHz in narrow-band (CL), wide-band (CW), low-noise low-frequency (FL), coaxial-resonator and other variants, and its selection table shows how tuning width costs phase noise. The narrow-band CVCO55CL-0090-0100 covers 90–100 MHz on 0.5–4.5 V with a Kvco of 8 MHz/V and −119 dBc/Hz at 10 kHz offset; the low-noise CVCO55FL-0075-0085 covers 75–85 MHz with 5 MHz/V and −123 dBc/Hz; the wide-band CVCO55CW-0100-0200 covers 100–200 MHz on 0–5 V with 25 MHz/V and −100 dBc/Hz. Typical entries list output power of about +5 to +9 dBm, second harmonics of −10 to −20 dBc, a 5 V supply at 25 mA maximum, and −40 to +85 °C operation. [4]

Editorial calculation: widening coverage tenfold, from a 10 MHz band to a 100 MHz band, raises Kvco from 5–8 MHz/V to 25 MHz/V and costs about 19–23 dB of phase noise at 10 kHz (−119 or −123 against −100 dBc/Hz). With 25 MHz/V, 1 mV of tuning-line noise moves the output 25 kHz, against 5–8 kHz on the narrow-band parts, so choose the narrowest band your channel plan allows and confirm the tuning range at the ends of your loop's voltage swing. [4] [3]

04

Trace what the data sheet defines

This is a functional reference built from the sources cited; it is not one maker's design.

05

Fill the specification fields with values for your design

A VCO selection needs values for your synthesiser. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the band, loop and noise data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Band: [frequency range]
Loop: [tuning voltage range; sensitivity; PLL IC]
Noise: [phase noise at offsets; spurious]
Output: [power; load]
Stability: [pushing; pulling; temperature]
Supply: [voltage; current]
Package: [case; footprint]
Volume: [quantity; lifetime]

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