BB145B - Low-Voltage Varactor Diode 2.75pF SOD-523 | NXP
MPN: BB145B β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.12 | $0.12 |
| 10 | $0.12 | $1.20 |
| 100 | $0.11 | $11.00 |
| 500 | $0.1 | $50.00 |
| 1,000 | $0.09 | $90.00 |
| 3,000 | $0.08 | $240.00 |
BB145B Overview
A varactor diode, also called a varicap or tuning diode, is a diode operated in reverse bias so that its depletion-region capacitance varies predictably with the applied voltage. Within the component hierarchy it belongs to the discrete semiconductor family, under diodes, alongside switching, rectifier, and Zener types. Varactors are the standard capacitance-tuning element in voltage controlled oscillators (VCOs), RF filters, and tunable matching networks, replacing mechanically variable capacitors in nearly all modern RF circuitry.
Key features of the BB145B include the ultra-small SOD-523 footprint that minimizes board area and parasitic inductance, a well-defined C4 of 2.75 pF with ratio 2.4 for predictable tuning slope, and low series resistance which directly improves loaded Q factor in oscillator tank circuits. The planar process yields tight capacitance distribution and stable behavior over temperature.
Technically, the tuning voltage modulates the depletion width of the planar junction, continuously varying junction capacitance between maximum and minimum values set by the doping profile. Because the device is specified for low-voltage operation, it suits portable and battery-powered RF front ends where tuning rails are limited to a few volts. The operating temperature range spans -55 C to +150 C per distributor data.
Typical applications are voltage controlled oscillators for wireless transceivers, tunable LC filters, and capacitance trimming in RF matching circuits for products operating in VHF and UHF bands.
In design, place the varactor directly at the tank inductor with short traces, DC-block it from the resonant circuit with a capacitor, and feed the tuning voltage through a high-value resistor to preserve Q; remember that tuning-voltage noise appears directly as phase noise.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for BB145B 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:
BB145B,115
β Drop-Inβ In Stock
$0.12 / Unit
View Datasheet βBB145B-01
β Drop-Inπ Reference alternative (not in catalog)
BB145,115
β Drop-Inπ Reference alternative (not in catalog)
BB145B Maximum Ratings & Electrical Characteristics
| Device Type | Low-voltage variable capacitance diode (varactor) |
| Technology | Planar |
| Capacitance C4 (at VR = 4 V) | 2.75 pF |
| Capacitance Ratio | 2.4 |
| Continuous Reverse Voltage | 6 V |
| Configuration | Single |
| Mounting Type | Surface Mount |
| Package | SOD-523 (SC-79) |
| Number of Terminals | 2 |
| Operating Temperature Range | -55 C to +150 C |
| Application | Voltage controlled oscillators (VCO) |
| Packaging | Reel 7 inch (Q1/T1) |
| Standard Package Quantity | 3000 |
| Min Order Quantity | 3000 |
BB145B Pin Configuration
| Pin 1 | Cathode β Cathode terminal, identified by band marking; connects to tuning bias node |
| Pin 2 | Anode β Anode terminal; junction capacitance appears between anode and cathode |
Typical Applications
BB145B is suitable for 6 applications: Voltage Controlled Oscillators (VCO), Tunable LC Filters, RF Matching Network Trimming, Portable and Battery-Powered Radio Front Ends, Test and Measurement Instrument Tuning, Automotive and Industrial RF Links.
Voltage Controlled Oscillators (VCO)
Voltage controlled oscillators are the primary listed application of the BB145B. The varactor junction capacitance of 2.75 pF at 4 V bias, varying with a ratio of 2.4 across the tuning range, directly sets the LC tank frequency as tuning voltage changes. Its low series resistance preserves tank loaded Q, which suppresses phase noise, the dominant quality metric in transceiver local oscillators. Because the device is a 6 V-class low-voltage varactor, it suits battery-powered VHF/UHF VCOs where the tuning rail is limited to a few volts. In layout, connect the varactor to the tank inductor with short traces and DC-block it from the resonant loop; feed the tuning voltage through a high-value resistor so the control network does not load the tank and degrade Q.
Recommended
Tunable LC Filters
In electronically tuned bandpass and lowpass filters, the BB145B varies the effective tank capacitance to shift the center frequency under control-voltage command. The 2.75 pF nominal capacitance at 4 V and the 2.4:1 capacitance ratio give approximately a sqrt(2.4) β 1.55:1 frequency tuning span in a single-inductor LC section, useful for multi-band receivers covering adjacent bands without switched inductor banks. Low series resistance is the critical parameter here because varactor ESR is usually the largest loss contribution in the filter passband, so it directly determines insertion loss and loaded Q. Place the varactor at a low RF-voltage node of the filter and decouple the bias network with a large resistor or RF choke to prevent control-line feedthrough.
Recommended
RF Matching Network Trimming
Antenna matching networks in portable wireless devices benefit from the BB145B as an adjustable shunt or series capacitance. Antenna impedance shifts with housing, hand position, and frequency, and a varactor-trimmed matching section lets firmware retune the network over the 2.4:1 capacitance span to hold return loss within specification. At 2.75 pF nominal, the BB145B suits the small capacitance values typical of compact antennas in the VHF/UHF and low microwave bands. Designers should keep RF swing across the varactor below the 6 V reverse-voltage class limits to avoid forward conduction and harmonic generation, and bias the device through a resistor network that presents high impedance at the operating frequency.
Recommended
Portable and Battery-Powered Radio Front Ends
The 6 V-class low-voltage rating of the BB145B makes it a natural fit for portable receivers and transceivers powered from single-cell or low-rail supplies, where legacy varactors requiring 20-30 V tuning rails are impractical. Operating from -55 C to +150 C, it withstands both outdoor automotive-adjacent environments and the elevated temperatures near power stages. Its SOD-523 footprint is among the smallest discrete RF packages, conserving PCB area in handset and IoT radio layouts and minimizing series inductance that would otherwise limit usable frequency. In these designs the varactor typically tunes the local oscillator or first IF filter, with the tuning DAC or PWM-derived voltage filtered to reduce phase-noise contribution from the control line.
Recommended
Test and Measurement Instrument Tuning
Signal generators, sweep oscillators, and spectrum-analyzer front ends use varactors like the BB145B for electronically swept tuning across VHF/UHF ranges. The planar process gives a repeatable, monotonic C-V curve with a defined C4 of 2.75 pF, which simplifies calibration of tuning-slope tables in firmware-controlled instruments. Low series resistance supports the high-Q tanks needed for clean spectral output, and the -55 C to +150 C operating range provides margin over instrument internal temperature gradients. For wide tuning spans, designers combine the BB145B with back-to-back varactor pairs to cancel even-order distortion and halve the RF voltage across each junction, improving linearity in the instrument's oscillator.
Recommended
Automotive and Industrial RF Links
Remote keyless entry, tire-pressure monitoring, and industrial short-range radio modules operate in VHF/UHF bands where the BB145B tunes the PLL loop VCO. The wide -55 C to +150 C temperature range covers under-hood-adjacent and industrial module environments, and the planar die provides stable capacitance over temperature so the PLL can hold lock without frequent retune. The 2.75 pF C4 value suits the compact tank inductors used in SMD module designs, and the low series resistance keeps oscillator phase noise within receiver blocking specifications. Verify the qualified ordering code (such as BB145B,115 availability) against your automotive sourcing requirements, since base-code lead times reach 99 weeks.
Recommended
Recommended Products Summary
Engineering reference data for BB145B β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BB145B,115 | BB145B-01 | BB145,115 |
|---|---|---|---|---|
| Package | SOD-523 (SC-79) | SOD-523 (SC-79) - same | SOD-523 (SC-79) - same | SOD-523 (SC-79) - same |
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors |
| Capacitance C4 (at 4 V) | 2.75 pF | 2.75 pF | 2.75 pF | 2.75 pF (wider tolerance band, non-B grade) |
| Availability | Reel, MOQ 3000, 99-week lead time | In stock at DigiKey, ships today | Stock varies by distributor | Stock varies by distributor |
Key Differentiators
- Stocked drop-in availability (vs BB145B (base code))
- Tighter capacitance grade than family sibling (vs BB145,115)
- Low-voltage 6 V tuning class (vs BB145B-01)
Design Notes
Keep the varactor loop inductance minimal: place the BB145B directly adjacent to the tank inductor with traces shorter than 2-3 mm at UHF. The SOD-523 body contributes roughly 1 nH of series inductance from pads alone, which at 1 GHz adds about 6 ohms of reactance - significant relative to a 2.75 pF reactance of about 58 ohms. Use via fences to a solid ground plane beneath the tuning node to confine fields and reduce coupling of tuning-line noise into the tank.
Bias the BB145B cathode through a high-value resistor (typically 10k-100k ohm) from the tuning DAC and decouple with an RC low-pass filter. Tuning-line noise modulates junction capacitance directly and appears multiplied by the tank slope as oscillator phase noise. Do not route digital clocks near the tuning node. In back-to-back pairs for linearity, the RF swing across each diode halves, keeping the 6 V reverse-voltage class respected with margin.
Do not let the RF voltage across the BB145B forward-bias the junction at the tuning-voltage minimum: with a 6 V-class device, large tank swings near zero bias cause rectification, harmonics, and Q collapse. Verify the C-V curve in-circuit because board parasitics add roughly 0.5-1 pF in parallel, shifting the effective tuning ratio below the datasheet 2.4. Also note the 99-week factory lead time on the base code; design in the stocked BB145B,115 code from the start.
Compliance Information
Retrieved data did not explicitly state RoHS/REACH/lead-free status for BB145B; verify on the official NXP product page before RoHS-bound production use.
