BB208 - Low Voltage Varactor Diode 10V 19.9pF | NXP
MPN: BB208 β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.16 | $0.16 |
| 10 | $0.15 | $1.50 |
| 100 | $0.13 | $13.00 |
| 500 | $0.11 | $55.00 |
| 1,000 | $0.09 | $90.00 |
| 3,000 | $0.07 | $210.00 |
BB208 Overview
A varactor diode (also called a tuning diode, varicap, or voltage-variable capacitor) is a semiconductor device that functions as an electrically controllable capacitance. In the signal-chain hierarchy it sits among discrete RF semiconductors, alongside RF diodes and switching diodes, and is a fundamental building block of voltage-controlled oscillators, tuning networks, and phase-locked loop (PLL) frequency-control circuits.
Key features of the BB208 family include its low reverse capacitance (19.9 pF nominal at 3 V per distributor/manufacturer data), a 10 V reverse-voltage rating suitable for battery-powered designs, and the small SOD-523 footprint that saves board area versus larger SOD-323 or SOT-23 varactors. The low tuning voltage requirement makes it well matched to 3.3 V and 5 V systems without dedicated high-voltage bias rails.
The device uses a junction profile engineered to deliver a useful capacitance-voltage slope, providing tuning ratio between low and high reverse-bias operating points. As a two-terminal passive-semiconductor element it adds no switching noise of its own and draws only the tiny reverse leakage current of the junction, simplifying bias-network design in VCO and tuned-amplifier circuits.
Typical applications include LC tank tuning in RF VCOs for receivers and transmitters, antenna matching and tunable filter networks, RF ID and short-range wireless front ends, and test-and-measurement tuned circuits where a compact, low-voltage tuning element is required.
A key design consideration is the bias network: a high-value series resistor (typically 10 kOhm or higher) between the tuning voltage source and the diode prevents loading of the resonant circuit, and the tuning voltage must always remain reverse-biasing relative to the RF swing across the diode.
This page synthesizes verified distributor data, family cross-references within the NXP BB208 series, and practical varactor bias-design notes not found in a single manufacturer datasheet.
Drop-in alternatives for BB208 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:
BB208-02
β Drop-Inπ Reference alternative (not in catalog)
BB208-03
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
BB208 Maximum Ratings & Electrical Characteristics
| Device Type | Varactor Diode (Variable Capacitance / Tuning Diode) |
| Capacitance (Cd) | 19.9 pF |
| Reverse Voltage (VR) Max | 10 V |
| Configuration | Single, 2-pin |
| Package | SOD-523 |
| Mounting Type | Surface Mount |
| Pins | 2 |
| Application | Low voltage variable capacitance (RF tuning) |
| Family | BB208 Series (BB208-02, BB208-03) |
| RoHS Status | unknown |
BB208 Pin Configuration
| Pin 1 | Cathode β Cathode terminal - connect to tuning voltage (reverse bias) via isolation resistor |
| Pin 2 | Anode β Anode terminal - typically RF/AC ground in tuning applications |
Typical Applications
BB208 is suitable for 6 applications: RF VCO Tuning, Tunable LC Filter, Antenna Matching Networks, Portable and Battery-Powered Receivers, Phase-Locked Loop Frequency Control, Test and Measurement Tuned Circuits.
RF VCO Tuning
The BB208's 19.9 pF nominal capacitance and low 10 V reverse-voltage class make it a natural tuning element in the LC tank of a voltage-controlled oscillator. Connected with its anode at RF ground and its cathode driven through a 10 kOhm or larger bias resistor from the tuning-voltage source, its junction capacitance forms part of the resonant tank and varies with tuning voltage, shifting the oscillation frequency. Because the BB208 is a passive junction device, it injects no switching noise; the oscillator phase-noise floor is set mainly by the varactor Q and the bias-network noise. The low tuning-voltage requirement suits 3.3 V PLL/VCO systems in portable receivers and short-range transmitters.
Recommended
Tunable LC Filter
Electronically tunable band-pass and notch filters use varactors such as the BB208 in place of switched capacitor banks to move their center frequency continuously. Placed in the resonant branch with a DC bias superimposed through a high-value isolation resistor, the 19.9 pF capacitance allows filter tuning across useful VHF/UHF ranges as the reverse voltage is varied from near 0 V up to several volts, always staying below the 10 V maximum. The SOD-523 package keeps parasitic series inductance low, preserving the filter Q at RF. Designers should account for the capacitance-versus-RF-swing nonlinearity at large signal levels to avoid distortion in high-power filter paths.
Recommended
Antenna Matching Networks
Adaptive antenna-tuning circuits in mobile and IoT transmitters use varactors to compensate for antenna impedance changes caused by hand position, proximity to objects, or frequency hopping. The BB208's low-voltage operation lets the matching network be driven directly from a DAC-generated tuning voltage without a charge pump, and its small SOD-523 footprint allows placement immediately at the antenna feed point where parasitics matter most. With 19.9 pF nominal capacitance and the 10 V rating, the diode covers the capacitance range typically required for small-loop and PIFA matching at VHF/UHF. The passive junction adds negligible loss when operated at adequate reverse bias for good Q.
Recommended
Portable and Battery-Powered Receivers
The BB208 family was developed specifically as a low-voltage variable capacitance diode, which aligns with battery-powered RF front ends operating from single-cell or 3.3 V/5 V rails. In handheld scanners, RF ID readers, and compact transceivers, the varactor tunes the local oscillator or input preselector under MCU/DAC control, replacing bulky mechanically variable capacitors. Its 10 V reverse rating provides comfortable margin against 3-cell stacks and transients, while the SOD-523 package supports dense PCB layouts. Because varactor leakage is only junction reverse leakage, tuning networks draw essentially no static current, preserving battery life in always-on monitoring receivers.
Recommended
Phase-Locked Loop Frequency Control
In PLL-based synthesizers, the BB208 serves as the loop's tuning element: the charge-pump output, filtered by the loop filter, drives the varactor and steers the VCO to lock onto the crystal-referenced phase. The 19.9 pF capacitance and its C-V slope determine the VCO tuning constant (Kvco in MHz/V), which directly shapes loop bandwidth and phase-noise trade-offs. Keeping tuning voltage in the higher-reverse-bias region improves linearity and Q; the 10 V rating permits loop-filter swing designs that avoid the low-bias high-capacitance region where Q degrades. The SOD-523 package minimizes series inductance for VHF-to-low-UHF synthesis.
Recommended
Test and Measurement Tuned Circuits
Bench instruments and lab prototypes use the BB208 in tunable RF oscillators, sweep generators, and alignment aids where electronic frequency control is more convenient than mechanical adjustment. The documented 19.9 pF nominal capacitance and 10 V limit allow straightforward calculation of tuning range with standard LC formulas before building the circuit, and the low-cost 2-pin SOD-523 device makes experimentation cheap. For widest tuning range, bias near the low end of the reverse-voltage range; for best Q and linearity, bias higher. Engineers should add RF-safe bias decoupling and measure the actual installed C-V curve, since PCB parasitics shift the effective tuning range.
Recommended
Recommended Products Summary
Engineering reference data for BB208 β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BB208-02 | BB208-03 |
|---|---|---|---|
| Package | SOD-523 (2-pin) | SOD-523 (2-pin) - same | SOD-523 family - same |
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors |
| Device Type | Varactor diode (single) | Varactor diode (single) | Varactor diode (single) |
| Nominal Capacitance | 19.9 pF | 19.9 pF | 19.9 pF (family datasheet) |
| Max Reverse Voltage | 10 V | 10 V | 10 V (family datasheet) |
| Configuration | Single 2-pin | Single 2-pin | Single 2-pin |
| Lifecycle Status | Family active; base code legacy | Active (NXP current product) | Active (NXP family variant) |
Key Differentiators
- Low-voltage tuning capability (vs BB208-02 (family baseline))
- Small SOD-523 footprint (vs BB208-02 (same))
- Guaranteed sourcing continuity via family codes (vs BB208-02)
Design Notes
Keep the series tuning inductor and the BB208 loop as small and symmetric as possible; the SOD-523 package has very low parasitic inductance, but PCB pad and trace inductance easily dominate at VHF/UHF. Use a solid ground plane under the tank area, place the bias isolation resistor (10 kOhm or larger) close to the diode cathode, and add an RF bypass capacitor from the bias node to ground to keep tuning-voltage noise out of the oscillator and preserve phase noise.
Operate the BB208 always in reverse bias: the cathode must remain positive relative to the anode including the RF voltage swing across the diode. Verify that the sum of the tuning voltage and the peak RF swing stays below the 10 V maximum rating. Forward-biasing even momentarily clamps the tank and creates harmonic distortion; operating at very low reverse bias (< 0.5 V effective) reduces Q and increases tuning nonlinearity.
Do not substitute a different varactor family based on nominal capacitance alone: the tuning range depends on the full capacitance-voltage curve and capacitance ratio, not the single-point value. Also, when sourcing legacy BB208 demand, order the current NXP ordering codes (BB208-02/BB208-03) and confirm the SOD-523 footprint matches older BB208 landing patterns before layout reuse. Note the 99-week NXP lead time (as of 2026-09-14) and stock accordingly.
Compliance Information
Compliance status not stated in the retrieved data. NXP product pages typically provide RoHS/REACH data per ordering code; verify on the NXP BB208-02 product page for the exact ordering code being purchased.
