• TI Thinks Resolved

Low power pir design

Prodigy 10 points

Replies: 2

Views: 82

Looking for best ultra low power pir design, I see designs such as TIDA 00489, 01069, 01398

Which is the best one, or are there any  others suitable for a new design.

Range / Sensitivity / ultra low current is most important

Typically 2uA

  • Hello Alan,

    I feel that the term 'best' is relative.  It really depends on the design goals that you're trying to meet.  Each of those designs have different amplifiers and one of them (01069) has 2 PIR sensors.  Here are my observations on each design:

    00489:  Uses 2 separate op amps for filtering and window comparator (LPV802 and TLV3691).  Uses CC1310, sub 1-GHz MCU.  This design will likely be slightly larger due to using different op amps for filtering and the comparator.

    01398:  Uses a single quad channel op amp (TLV8544) for both filtering and comparator functions.  Uses CC2650, 2.4GHz MCU.  Likely smaller solution size than the first one.

    Note that there is a table in each of these designs that compares specifications like current, motion sensing range, radio transmission range, etc.  You'll notice that the design that uses the LPV802/TLV3691 seems to consume less current, but as I mentioned earlier I believe the solution size will be slightly larger.  

    For 01069, the first thing to note is that it uses a AAA battery instead of coin cell, so this design will likely be larger than the other two.  Secondly, it uses 2 PIR sensors instead of one in order to help reduce false triggers.  Once could make the case that if you have fewer false triggers, it could be the lowest power design of them all but at the expense of size.

    To answer your question directly, they all appear to have the same range (30').  00489 and 01398 will be more sensitive since they have 1 PIR sensor, whereas 01069 has 2 sensors for false trigger reduction.  Finally, 00489 ultimately has the longest battery life (unless you decide using 2 PIR sensors to reduce false triggers will yield an even longer battery life).  All in all it really depends on your application and particular situation.

    I hope this helps!

    Regards,

    Pete Semig

    General Purpose Amplifier Applications

  • Alan,

    The PIR detector itself is the largest power consumer if used per it it's datasheet. The PIR detector has an internal FET preamplifer, similar to a condenser microphone capsule, that requires an external resistor to the power source. This resistor sets the FET biasing current. The more current, the quieter the noise.

    In our PIR designs we did "starve" the internal FET preamplifier to get the current below 1uA. Doing this significanlty raises the noise level of the sensor, which in turn increases the noise floor which decreases the effective detection distance.

    Since the "front end" determines the overall system signal-to-noise level, the sensor noise level dominates the system S/N level.

    If you want a better detection distance, then you either burn more current in the PIR detector to reduce the noise, or, reduce the upper cutoff frequency of the filter. Reducing the upper cutoff frequency will reduce the sensitivity to "fast' moving objects (you could theoretically run past the sensor w/o tripping).

    So, there are several knobs to twist, and each one has compromises. So you essentially have a total range to power consumed tradeoff you need to decide.

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group