by Neal Kurfiss and Michael Jackson
Previous blogs in this series looked at motor control, power, and connectivity options for surveillance cameras. In this blog, the focus switches to how including additional non-optical sensors can augment the effectiveness of surveillance cameras, especially for security applications, by providing them with more ‘senses’ than vision alone.
Limitations of Camera Vision
Critical to the overall integrity of a surveillance camera solution is its ability to operate effectively in all types of weather conditions. Even camera systems with the highest quality image sensors can struggle to maintain their range and fidelity in harsh weather conditions like heavy rain and fog. This impacts their effectiveness, especially in security applications, presenting intruders with a vulnerability they can potentially take advantage of.
Furthermore, surveillance cameras are commonly used to trigger a response to an incident occurring within its field of view. While widening the viewing angle is the logical approach, it complicates event verification due to the difficulty in resolving detail and this often results in false positive alarms. While zooming the camera to focus on one area can reduce the chances of this happening, it causes the primary vision system to miss events in other areas, potentially leading to false negatives which reduce the effectiveness of the security application.
Radar Sensors Give Cameras an Added ‘Sense’
Including additional sensors makes cameras smarter by helping direct their focus onto regions of interest, by sensing events that occur outside of the field of vision. 24GHz radar sensors can provide this functionality with the extra benefit of broad-range objection detection that operates in all types of weather conditions. For a radar system to operate in conjunction with a surveillance camera, the radar system must have the following features:
- Long Range
- Excellent resolution
- The ability to detect people from long distances
- Small form factor
- Attachable to a camera (or on a pole with a connection to the camera)
ADI‘s ‘Tinyrad’ 24GHz FMCW 2T4R (Figure 1) platform meets all of these requirements. This solution features 2 transmit and 4 receive channels/antennas. This designation is 2T4R. These antennas can be printed onto a PCB. The Tinyrad solution has a range resolution of 70 cm which is sufficient for detecting human presence. It has a small form factor (credit card size of 85 mm × 55 mm). The ADF5901/2 transmitter and ADF5904 receivers are fully integrated allowing for a simplified PCB design and have a range of 100 m. The ADF5901 is a 24 GHz Tx monolithic microwave integrated circuit (MMIC) with an on-chip, 24 GHz VCO with PGA and dual Tx channels for radar systems. It has a 24 GHz VCO that generates the 24 GHz signal for the two Tx channels and the local oscillator (LO) output. Each Tx channel contains a power control circuit, and it also includes an on-chip temperature sensor. The ADF5904 is a 4-channel, 24 GHz, receiver downconverter in which each channel contains a single-ended RF input with an on-chip balun followed by a differential low noise amplifier (LNA) and a downconverter mixer with differential output buffers. The RF LO path also has an on-chip balun.
Figure 1 ADI’s 24 GHz FMCW MIMO Radar (TinyRad)
Exceptional Range and Resolution
The exceptional range and resolution of this platform are made possible using the industry-leading ADF4159/8 PLL and Fractional-N Frequency Synthesizer. This is a 13 GHz, fractional-N frequency synthesizer with modulation and both fast and slow waveform generation capability. The part uses a 25-bit fixed modulus, allowing subhertz frequency resolution. It consists of a low-noise digital phase frequency detector (PFD), a precision charge pump, and a programmable reference divider. The Σ-Δ-based fractional interpolator allows programmable fractional-N division.
Figure 2 Block diagram of ADI's radar platform solution
The final blog in this series will explore the benefits audio brings to surveillance cameras.