Diodes Incorporated ZC933TC

Overview

ZC933TC from Zetex Semiconductors is a 12 V hyperabrupt silicon varactor diode in SOT23 package, optimized for voltage-controlled oscillator (VCO) and temperature-compensated crystal oscillator (TCXO) tuning. It delivers 42.0 pF capacitance at 1 V, 18.0 pF at 2.5 V, and 12.0 pF at 4 V reverse bias, with minimum Q of 150 at 50 MHz and typical reverse leakage of 200 pA - enabling low-phase-noise RF frequency synthesis in wireless transceivers.

For engineers reviewing the ZC933TC datasheet, ZC933TC pinout, ZC933TC application, or ZC933TC equivalent, key selection criteria include its octave-tuning range (0–6 V), hyperabrupt C-V slope for linear frequency vs. voltage response, low IR for minimal oscillator drift, high Q at VHF/UHF bands, and SOT23 footprint compatibility with compact RF front-end layouts.

Technical Context

This varactor operates as a voltage-dependent capacitor in resonant tank circuits, where applied reverse bias modulates junction depletion width to shift oscillation frequency. Its hyperabrupt doping profile yields a C ∝ V^−γ relationship with γ ≈ 2.0–2.5, supporting wide, monotonic tuning across 0–6 V without capacitance discontinuities.

Designed for stable operation at 25°C ambient, it maintains tight C-V tolerance (±10% typical), exhibits −300 to −400 ppm/°C temperature coefficient of capacitance at 3 V, and sustains rated performance up to 12 V reverse breakdown - critical for TCXO loop stability and phase noise floor control in mobile radio synthesizers.

Key Specifications

Pinout & Package

SOT23 package: 3-pin plastic surface-mount case with gull-wing leads; cathode marked by beveled edge or dot; standard JEDEC MO-215 outline; body dimensions 2.9 × 1.3 × 1.0 mm (L × W × H).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar varactor diode applications.

Compared with BBY52-02W and SMV1232-011, ZC933TC offers the widest capacitance range (42–12 pF) and highest low-voltage capacitance - making it optimal for octave-tuned VCOs below 1 GHz where tuning linearity and bias headroom are prioritized over ultimate Q or leakage.

Availability

ZC933TC is available at Aetrix Electronics and suitable for VCXO design, TCXO compensation networks, mobile radio VCOs, and ISM-band tunable filters requiring stable component supply with traceable lot history and full RoHS compliance.

Supply support for ZC933TC includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Zetex Semiconductors plc (now part of Diodes Incorporated) was a UK-based designer of high-performance analog and RF semiconductors, specializing in discrete transistors, diodes, and interface ICs for industrial and communications markets.

The ZC930–ZC934 series targets RF frequency control applications, with ZC933TC specifically engineered for wide-range, low-noise varactor tuning in cost-sensitive portable and infrastructure wireless systems.

FAQ

What is the maximum recommended reverse voltage for continuous operation of ZC933TC?

The absolute maximum reverse voltage is 12 V, but for reliable long-term operation in TCXO or VCO circuits, Zetex specifies 8 V as the maximum recommended DC bias. Exceeding 8 V increases reverse leakage exponentially and accelerates junction degradation, particularly above 85°C ambient.

Does ZC933TC require external series resistance in the tuning line?

Yes - a 10–100 kΩ series resistor is recommended between the tuning voltage source and the anode to limit current during transient events and prevent forward conduction if the control voltage exceeds 0.7 V. This protects the junction and stabilizes bias point against noise coupling in RF-dense environments.

Can ZC933TC be used in dual-common-cathode configuration?

No - ZC933TC is a single-diode device in SOT23 package. Dual common-cathode variants (e.g., ZC933ATA) exist in the same series but use SOD-323 packaging with separate anode terminals; ZC933TC has only one functional junction and no internal cathode sharing.

How does temperature affect the C-V curve of ZC933TC?

Capacitance decreases linearly with rising temperature at fixed bias due to negative temperature coefficient of −300 to −400 ppm/°C. At 3 V bias, capacitance drops ~0.35 pF per 10°C rise - a key factor requiring compensation in TCXO designs using this varactor in the control loop.