BB202 - Low-Voltage Varactor Diode 30.5pF | NXP | FM VCO Tuning
MPN: BB202 β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.3 | $0.30 |
| 10 | $0.27 | $2.70 |
| 100 | $0.22 | $22.00 |
| 500 | $0.18 | $90.00 |
| 1,000 | $0.15 | $150.00 |
BB202 Overview
A varactor diode, also called a variable capacitance diode or varicap, is a semiconductor device whose junction capacitance varies with the applied reverse-bias voltage. Within the diode family hierarchy (diode -> varactor -> voltage-controlled capacitance element), varactors act as electrically tunable capacitors in LC resonant circuits, replacing mechanical tuning capacitors in radio-frequency systems. They are a core building block of voltage-controlled oscillators (VCOs), PLL frequency synthesizers, and RF tuners.
Key features of the BB202 include a very steep capacitance-to-voltage (C/V) curve, which delivers large frequency deviation per volt of tuning voltage in VCO designs; a C0.2 to C2.3 ratio of at least 2.5 for wide tuning range; very low series resistance, which preserves resonant circuit Q factor and minimizes phase noise contribution; and planar technology fabrication for stable, repeatable capacitance characteristics.
The steep C/V curve combined with low series resistance makes the BB202 particularly suited to battery-powered FM radio electronic tuning, where tuning voltage rails are limited to a few volts. Because the capacitance swing is concentrated at low reverse voltages, designers can cover the FM band (87.5 to 108 MHz) with tuning voltages below 3 V, simplifying power-supply design in portable receivers and low-voltage RF front ends.
Typical applications include electronic tuning in FM radio receivers, voltage-controlled oscillators in PLL synthesizers, and low-voltage RF tunable filter circuits.
Design consideration: bias the cathode with a clean, RF-decoupled tuning voltage; any ripple or noise on the tuning line modulates the VCO frequency directly, so use RC filtering and separate the bias network from the resonant tank.
This page synthesizes verified datasheet parameters, drop-in alternative analysis, and practical design notes not consolidated in the manufacturer short datasheet.
Drop-in alternatives for BB202 β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
BB201
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
BB204
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
BB212
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
BB202 Maximum Ratings & Electrical Characteristics
| Product Type | Low-voltage variable capacitance diode (varactor) |
| Capacitance at 0.2 V (C0.2) | 30.5 pF |
| Capacitance at 2.3 V (C2.3) | 9.5 pF |
| Capacitance Ratio (C0.2/C2.3) | min. 2.5 |
| C/V Curve | Very steep |
| Series Resistance | Very low |
| Maximum Reverse Voltage | 6 V |
| Configuration | Single |
| Mounting Type | Surface Mount |
| Package | SOD523 (SC-79), 2-pin ultra-small SMD plastic |
| Technology | Planar |
| Primary Applications | Electronic tuning in FM radio; VCO |
| Ordering Code | BB202,115 |
BB202 Pin Configuration
| Pin 1 | K (Cathode) β Cathode; connect to positive tuning/bias voltage |
| Pin 2 | A (Anode) β Anode; connect to LC resonant tank side |
Typical Applications
BB202 is suitable for 6 applications: FM Radio Electronic Tuning, Voltage-Controlled Oscillators (VCO), Tunable LC Filters, Portable Battery-Powered Receivers, PLL Frequency Synthesizer Loops, RF Parametric and Test Circuits.
FM Radio Electronic Tuning
The BB202 is purpose-built for electronic tuning in FM radio receivers, as stated directly in the NXP datasheet. Its very steep C/V curve swings from 30.5 pF at 0.2 V to 9.5 pF at 2.3 V, allowing the full 87.5 to 108 MHz broadcast band to be covered with tuning voltages below 3 V, ideal for battery-powered portable radios. The diode is placed in the local-oscillator LC tank, with the cathode driven by a filtered tuning voltage from a DAC or PLL charge pump. Very low series resistance preserves tank Q, keeping phase noise and channel selectivity within spec. A high-value bias resistor isolates the tuning line from the RF swing so capacitance is set by DC bias alone.
Recommended
Voltage-Controlled Oscillators (VCO)
In a PLL-based VCO, the BB202 acts as the voltage-tunable capacitance element of the resonant tank. The minimum 2.5 ratio between C0.2 (30.5 pF) and C2.3 (9.5 pF) provides wide frequency deviation per tuning volt, while the very low series resistance keeps loaded Q high, which directly reduces oscillator phase noise - a critical parameter in frequency synthesizers. The diode is typically coupled to the tank inductor through a DC-blocking capacitor, with the cathode tied to the tuning voltage via an RF choke or 47k resistor. Designers should linearize the tuning slope by choosing the coupling ratio, since the steep C/V curve concentrates sensitivity at low bias voltages near 0.2 V.
Recommended
Tunable LC Filters
Low-voltage RF front ends can use the BB202 as an electronically tunable capacitance in LC band-pass filters, shifting the passband with a control voltage instead of switched capacitor banks. With 9.5 pF at 2.3 V and 30.5 pF at 0.2 V, a filter centered around a 100 nH inductor can sweep tens of percent in frequency across a 2 V control range. The very low series resistance is essential here because filter insertion loss scales inversely with component Q; a high-ESR varactor would add measurable passband attenuation. Place the diode where RF voltage swing is modest, since large signal swings partially cancel the DC bias and cause distortion in the filter response.
Recommended
Portable Battery-Powered Receivers
Because the BB202 develops its full tuning range below 3 V reverse bias, it fits single-cell and two-cell battery products where only a 3 V rail exists for both the oscillator and the tuning DAC. The SOD523 (SC-79) package occupies about 1.2 x 0.8 mm of board area, supporting miniaturized portable receiver designs. Planar technology fabrication gives stable capacitance over temperature and time, which keeps calibration drift low over battery life. Designers should derive the tuning voltage from a regulated reference rather than the raw battery rail, otherwise supply droop shifts oscillator frequency. Decouple the tuning node with at least 100 nF to suppress audio-frequency noise from the digital section.
Recommended
PLL Frequency Synthesizer Loops
In frequency synthesizers, the BB202 converts the PLL charge-pump output into the frequency control of the VCO tank. The steep C/V curve yields high tuning gain (MHz per volt), which raises loop gain and can improve lock speed, but designers must ensure the phase margin accounts for this sensitivity. The very low series resistance limits the varactor's own phase-noise contribution to the oscillator. Connect the diode via a second-order RC loop filter (for example 1k and 100 nF stages) so charge-pump ripple does not produce spurious sidebands. Because the effective capacitance is signal-dependent, keep the RF swing across the diode small relative to the DC bias for clean spectral performance.
Recommended
RF Parametric and Test Circuits
The BB202's well-characterized, repeatable capacitance points (30.5 pF at 0.2 V, 9.5 pF at 2.3 V) make it useful as a trim element in RF test fixtures, antenna matching networks, and lab tuners where a small DC-controlled capacitance is required. Very low series resistance means the part adds negligible loss when measuring network Q or antenna efficiency, unlike lossier generic switching diodes. In automated test equipment, a DAC-driven bias network sweeps the capacitance to null a match or peak a response. Ensure the bias supply is floating with respect to RF ground through a choke, and use short, low-inductance ground returns to preserve the diode's inherent Q at VHF frequencies.
Recommended
Recommended Products Summary
Engineering reference data for BB202 β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BB201 | BB204 | BB212 |
|---|---|---|---|---|
| Package | SOD523 (SC-79) | SOD523 - same | SOD523 - same | SOD523 - same |
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors |
| C/V Curve Character | Very steep | Steep (BB low-voltage family) | Steep (BB low-voltage family) | Steep (BB low-voltage family) |
| Series Resistance | Very low | Low (same family planar process) | Low (same family planar process) | Low (same family planar process) |
| Primary Application | FM radio tuning, VCO | Low-voltage tuning, VCO | Low-voltage tuning, VCO | Low-voltage tuning, VCO |
Key Differentiators
- Very steep C/V curve for maximum tuning deviation (vs BB201)
- Very low series resistance preserves tank Q (vs BB212)
- Ultra-small SOD523 footprint (vs BB201)
Design Notes
Noise on the tuning line frequency-modulates the VCO directly, because the BB202 capacitance follows the reverse-bias voltage instantaneously. Derive the tuning voltage from a dedicated reference or filtered DAC output, place an RC filter (for example 10k and 100 nF) close to the cathode, and route the tuning trace away from digital and switching nodes. In PLL systems, inadequate loop filtering of charge-pump ripple produces reference spurs whose level scales with the diode tuning gain, which is high at low bias given the steep C/V curve.
Use the standard SOD523 (SC-79) footprint with short, wide connections to the LC tank to minimize series inductance, which would reduce the effective tuning range at VHF. Keep the DC-blocking capacitor between the diode anode and the tank large enough (at least 10x the diode capacitance, e.g. 330 pF) that it does not dominate the series capacitance, and return the bias resistor to a quiet DC node. Place the diode at a low-RF-swing point of the tank to limit self-biasing effects.
Do not exceed the 6 V reverse voltage rating; low-voltage varactors like the BB202 are optimized for their steep curve below 3 V and degrade or shift capacitance permanently on overvoltage. Also remember the diode is polarized - reversing it forward-biases the junction and shorts the tank. When substituting another BB-family part, recalculate the tank inductor and coupling ratio, because the capacitance points differ between family members even though the package and pinout are identical.
Compliance Information
Compliance data not present in verified web data; BB202,115 ordering code is the current SMD standard offered at DigiKey. Consult NXP product page for RoHS/REACH declarations.
