CMX90A702QH Cross Reference Analysis 26.5-29.5 GHz RF Amplifier
The CMX90A702QH is a general-purpose medium-power RF amplifier from CML Microcircuits designed for the 26.5 GHz to 29.5 GHz frequency range, covering the n257 and n258 5G NR bands as well as portions of the Ka-band used in satellite communications. This surface-mount IC delivers 26.7 dBm typical P1dB output power and 20.5 dB small-signal gain from a 3 V to 4.2 V supply drawing 182 mA. Engineers evaluating alternatives within the RF Amplifiers category for mmWave transmitters or driver stages require a structured cross-reference methodology that addresses electrical specifications, footprint compatibility, and thermal behavior.
Core Electrical Specifications and Engineering Interpretation
| Parameter | Value | Engineering Meaning |
|---|---|---|
| Frequency Range | 26.5 GHz – 29.5 GHz | This parameter indicates the 3 dB bandwidth over which the amplifier maintains specified gain flatness. Typical range for mmWave 5G infrastructure is 24.25–29.5 GHz; this part covers the upper segment. |
| P1dB (Output) | 26.7 dBm | Output power at 1 dB gain compression. Values above 25 dBm are typically sufficient to drive a downstream high-power PA stage or to serve as a final stage in short-range point-to-point links. |
| Small-Signal Gain | 20.5 dB | This parameter indicates the linear voltage gain at 26.5 GHz. In mmWave chains, 18–22 dB per stage is common; lower gain would require additional pre-amplification stages. |
| Supply Voltage | 3.0 V – 4.2 V | Operating voltage range. A single Li-ion cell (3.6 V nominal) falls within this range, simplifying battery-powered equipment design. |
| Supply Current | 182 mA | Quiescent drain current. For a 3.6 V supply, this corresponds to approximately 655 mW DC power consumption – typical for a medium-power GaAs pHEMT stage at mmWave frequencies. |
| Test Frequency | 26.5 GHz | Specialty parameter — see datasheet. The manufacturer guarantees specifications at this frequency; performance at 29.5 GHz may differ slightly due to gain roll-off. |
| Package | 20-VFQFN Exposed Pad (4x4 mm) | Thermal and RF grounding is provided through the central pad. A 4×4 mm body with 0.5 mm pitch is a standard footprint shared by several CML and competitor mmWave amplifiers. |
The P1dB of 26.7 dBm places this amplifier in the medium-power class, suitable as a driver for external GaN or GaAs final-stage power transistors. The 20.5 dB gain means a single device can boost a typical 5 dBm modulator output to over 25 dBm, sufficient for local oscillator distribution or short-reach unlicensed links. Engineers should note that the 3 V minimum supply allows operation from regulated 3.3 V rails without a boost converter – a meaningful advantage in power-constrained small-cell or CPE designs.
Parameters Critical for Substitution vs Parameters That Can Be Relaxed
When evaluating a cross-reference for the CMX90A702QH, engineers must distinguish between mandatory electrical matches and parameters where modest deviation is acceptable. The table below summarizes this prioritization.
- Must match within ±10%: Frequency range (26.5–29.5 GHz), P1dB (±0.5 dB), small-signal gain (±1.5 dB), supply voltage range (3.0–4.2 V), package footprint (20-VQFN 4×4 mm with exposed pad). A substitute with a different package pitch or missing center pad will require PCB respin.
- Relaxable with analysis: Supply current (±15 mA is generally fine if thermal budget permits), test frequency (specs at 28 GHz are acceptable if 26.5 GHz performance is within 0.5 dB), and generic "General Purpose" RF type classification (devices tagged specifically for 5G or satellite are safe).
- Must NOT be relaxed: Operating frequency edges – a 24–27 GHz part cannot cover 29.5 GHz. Also the OIP3 or linearity rating, though not fully specified in this datasheet excerpt, should be verified from the datasheet curves. Differences beyond 2 dB in OIP3 will degrade EVM in OFDM waveforms.
For instance, the sibling parts CMX90G702QF or CMX90G301QF share the same package but cover different frequency bands; they are not drop-in substitutes unless the application band is narrower. Always verify the full S-parameter set from each candidate datasheet.
Cross-Reference Methodology Across Leading Brands
The RF amplifier market at 26–30 GHz is served by Qorvo, Skyworks, Analog Devices, MACOM, and Mini-Circuits, among others. A systematic cross-reference methodology involves three steps. First, filter candidates by package – only 20-VQFN 4×4 mm or equivalent with exposed pad. Second, compare bias conditions: if a competitor part requires a different drain voltage (e.g., 5 V) or a negative gate supply, it cannot directly replace the CMX90A702QH's single 3–4.2 V bias. Third, verify that the gain roll-off across temperature stays within the system budget. CML typically specifies gain flatness of ±0.5 dB across the band; some competitor parts may show ±1 dB, which can push cascaded stages beyond the link budget.
Specific brand comparisons must be made using each manufacturer's public datasheets. As an example, a Qorvo device with similar frequency coverage and 4×4 QFN package may offer higher gain but at the cost of 50% more current – acceptable in base station designs but problematic for battery-operated terminals. Mini-Circuits offers devices in the same band but often with wider voltage ranges; however, their gain at 29.5 GHz may drop faster due to different process technology. No generic "equivalent" part number should be assumed without a full S-parameter overlay from a VNA sweep.
Validation Steps: Electrical Consistency and Long-Term Reliability
Before committing a substitute amplifier into production, engineers should execute three validation phases. Phase 1 – Electrical consistency: Measure S11, S21, and S22 from 26 to 30 GHz using a calibrated VNA. Compare the gain ripple – the CMX90A702QH typically shows less than 0.3 dB ripple across the band. If a candidate shows ripple above 0.5 dB, it may cause frequency-dependent EVM degradation in OFDM or 256QAM signaling. Phase 2 – Temperature cycling: Run 100 cycles from -40°C to +85°C per JEDEC JESD22-A104. Measure P1dB and gain at 26.5 and 29.5 GHz after every 25 cycles. Devices with GaAs pHEMT processes (including CML) typically show less than 1 dB shift; SiGe BiCMOS alternatives sometimes exhibit 2 dB drift. Phase 3 – Long-term aging: Perform a 1000-hour accelerated life test at 85°C case temperature with nominal bias. Look for output power degradation exceeding 0.5 dB. Competitor parts with lower junction-to-case thermal resistance (RθJC) often outlast CML in hot environments – this is a legitimate advantage of some substitutes.
Supply-Chain Risk and Toolchain Compatibility
Sourcing the CMX90A702QH or its cross-references requires careful consideration of batch date codes and moisture sensitivity level (MSL). RF amplifiers in QFN packages are MSL-3 typically, meaning limited floor life after opening. Procurement professionals should demand parts from the same date code lot for production runs; mixing different batches can lead to gain variation of ±1 dB across boards due to process spread. Furthermore, evaluation board availability differs – CML offers a reference design but few third-party providers. Some MACOM and Mini-Circuits counterparts have wider evaluation ecosystem support and come with Gerber files and ADS simulation models. Engineers needing HFSS or ADS models for matching network design should prioritize candidates that provide these files, as the CMX90A702QH matching network design is non-trivial given the 26.5 GHz center frequency.
When NOT to Substitute the CMX90A702QH
There are legitimate scenarios where substitution is discouraged. If the design is already in production with validated matching networks and regulatory approvals (e.g., FCC part 15 for 28 GHz operations), swapping the amplifier may require re-optimization of the output matching network and re-testing for harmonic emissions. The CMX90A702QH's bias circuit stability at low voltage (3 V) is optimized by CML's internal regulation; competitors requiring higher minimum voltage (e.g., 4.5 V) could cause brownout in systems with 3.3 V rails under load. Additionally, if the application demands very low noise figure in the receive path (<1.5 dB), this part is not suited – it is a power amplifier, not an LNA. In that case, select a genuine LNA from the CML CMX90G series or from Skyworks/Qorvo.
Substitution Decision Matrix
| Condition | Recommendation | Risk Level |
|---|---|---|
| Same package, same frequency band, gain within 1.5 dB, P1dB within 0.5 dB, same bias range | Proceed with validation (Phase 1–2) | Low |
| Same package, but gain differs >2 dB or P1dB >3 dB lower | Redesign driver chain, not a drop-in | Medium |
| Different package (e.g., 5×5 mm) or voltage >4.5 V | PCB redesign required; high cost | High |
| Production design already qualified with CMX90A702QH | Retain original part unless supply disruption | Very low |
Frequently Asked Questions About CMX90A702QH
What is the typical application circuit for the CMX90A702QH?
The datasheet suggests a single-ended 50 Ω input and output with series DC-blocking capacitors (0.1 pF typical) and microstrip matching networks. The exposed pad must be soldered to a ground plane with multiple vias for thermal dissipation. Refer to the application note from CML for the full schematic and bill of materials.
Where can I find the CMX90A702QH S-parameters?
Full S-parameter files (S2P format) are available in the product's technical documentation section on the distributor's page or the manufacturer's support portal. These files cover 26–30 GHz and are suitable for ADS and AWR simulation tools.
How does the CMX90A702QH compare to the CMX90G702QF?
The CMX90G702QF is also a 26–30 GHz amplifier but in a 24-QFN package with different pinout. It offers similar gain but lower P1dB (around 24 dBm). They are not pin-compatible and cannot be cross-referenced without PCB layout changes.
Is the CMX90A702QH RoHS compliant?
Yes, the part is marked as RoHS compliant. The package uses lead-free solder terminals and the device is free of restricted substances per EU Directive 2011/65/EU.
Technical takeaway: When sourcing the CMX90A702QH or evaluating cross-references, always obtain the full S-parameter set and verify the gain flatness across the full temperature range. Prioritize parts with identical package and bias voltage requirements. For designs targeting 5G NR n257 (28 GHz), this amplifier is a solid choice; for n258 (26 GHz), ensure the candidate's lower band edge is at 25.5 GHz or below to provide adequate margin. Keep a minimum 5% frequency margin on both ends of the band to account for production variation.
