How do I design a logarithmic detector amplifier chain for ESM applications?
Logarithmic Detector for ESM Receivers
Logarithmic receivers are the backbone of passive electronic warfare systems. They provide amplitude measurement over a wide dynamic range without any AGC, making them ideal for measuring unknown signals in complex electromagnetic environments.
| Parameter | Superheterodyne | Direct Conversion | Digital IF |
|---|---|---|---|
| Image Rejection | 60-90 dB (filter) | 30-50 dB (mismatch) | N/A (digital) |
| DC Offset | No issue | Major issue | No issue |
| LO Leakage | Low | High | Low |
| Integration | Difficult | Easy (single chip) | Moderate |
| Dynamic Range | 80-120 dB | 60-90 dB | 70-100 dB |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
What are commercial log detector ICs?
Analog Devices has the most comprehensive log detector product line: AD8317: 1 MHz - 10 GHz, 55 dB dynamic range, 25 mV/dB slope. AD8318: 1 MHz - 8 GHz, 60 dB range, -24 mV/dB (negative slope for control loops). ADL5902: 50 MHz - 9 GHz, 65 dB range, true RMS responding. HMC1030: 0.5 - 30 GHz, 33 dB range (extended frequency for mmW). These ICs integrate the entire log amplifier chain, detectors, and summation network into a single chip. They replace multi-chip solutions that previously required separate amplifier dies, detector diodes, and bias networks.
What is a successive detection log video amplifier (SDLVA)?
The SDLVA is the formal name for the log detector chain described above. It is 'successive' because each stage detects in succession as the input power increases. 'Log video' refers to the output being a video-bandwidth (baseband) signal proportional to the log of the input power. SDLVAs are available as multi-chip modules from: Planar Monolithics (PMI), L3Harris, Akon Inc., and others. These modules cover 0.5-18 GHz with 70-90 dB dynamic range and 50+ MHz video bandwidth. Costs: $500 to $5000 per module depending on the performance and frequency range.
What is the pulse measurement capability?
ESM receivers must measure radar pulses with pulse widths of 50 ns to 100+ us. The log detector's video bandwidth determines the minimum measurable pulse width: for 10 ns rise time and 500 MHz video bandwidth: pulses as short as 50 ns can be measured with less than 1 dB amplitude error. For 100 ns rise time and 50 MHz video bandwidth: minimum pulse width approximately 200 ns. The log detector also measures: pulse amplitude (from the video output level, using the log slope), pulse width (from the video output duration), and pulse repetition interval (from the time between video pulses). These pulse descriptor words (PDWs) are the fundamental output of an ESM receiver.