APPLICATION NOTE AN9770 Rev 1.00 Engine Knock Sensing Applications (HIP9011EVAL1Z) Nov 6, 2006 There continues a driving effort by the Government and the HIP9011EVAL1Z Evaluation Board automotive industry to make cars more efficient with lower emissions. Tighter and more extensive control of automobile engines by microcontrollers has resulted in significant strides towards these goals. One of the factors contributing to these improvements is engine ignition control. The HIP9011 helps in the ongoing battle to enhance engine performance by providing more detailed information to the engine microcontroller. An important point to remember - automotive engines operate most efficiently when the engine is placed in the ignition timing condition just prior to ping or pre-ignition. The closer an engine can operate to this condition, the higher the performance. This is analogous to an operational amplifier, where the higher the gain, the lower the distortion. In the case of the knock signal processing IC, it provides a means of detecting engine knock or ping at levels that were previously unrealizable by amplification and filter means. Figure 1 shows the HIP9011 in a typical engine application. ENGINE CONTROL MODULE MOSI CS HIP9011 MOSI SO SCK INTOUT INT/HOLD A/D SPI CONVERTER INTERFACE HOST KNOCK MICROCONTROLLER KNOCK SENSOR SENSOR OTHER ENGINE SENSOR SIGNALS ENGINE CONTROL SIGNALS FIGURE 1. HIP9011 IN A TYPICAL ENGINE CONTROL APPLICATION AN9770 Rev 1.00 Page 1 of 15 Nov 6, 2006Engine Knock Sensing Applications (HIP9011EVAL1Z) CH0FB 18 CH0IN 19 DIFFERENTIAL - CH0NI 20 + PROGRAMMABLE PROGRAMMABLE TO SINGLE-ENDED PROGRAMMABLE GAIN BANDPASS ACTIVE INTOUT 4 CONVERTER, INTEGRATOR STAGE FILTER FULL WAVE CHIFB 17 40 - 600s SAMPLE AND 2 - 0.111 1 - 20kHz RECTIFIER 32 STEPS HOLD AND 64 STEPS 64 STEPS CH1IN 16 OUTPUT DRIVER - CH1NI 15 + OSCIN 9 PROGRAMMABLE DIVIDER CLOCK TO SWITCHED OSCOUT 10 CAPACITOR NETWORKS SCK 13 CS 8 POWER SUPPLY REGISTERS SPI SI 12 AND AND INTERFACE BIAS CIRCUITS STATE MACHINE SO 11 INT/HOLD 7 VMID 3 VDD 1 GND 2 TEST 14 FIGURE 2. SIMPLIFIED BLOCK DIAGRAM OF THE HIP9011, SINGLE CHANNEL KNOCK SIGNAL PROCESSING IC Operation of the Signal Processing IC The output of the Filter Stage in the HIP9011 is applied to a full wave rectifier and then to an integrator. The integrator operation Inputs from one or two piezoelectric sensors mounted on the is initiated by the INT/HOLD signal from the microcontroller. It is engine block are capacitively coupled to the inputs of the only during the rising edge of the INT/HOLD signal that the operational amplifiers within the HIP9011. Two sensors are integrator starts from its initial reset condition of 0.125V. shown in the examples in this application note, one for each Integration is towards the positive supply when a knock signal side of a V type of engine configuration. Engines configured is present. Severity of the knock signal and the integrators in-line may use sensors placed on either end of the engine programmable time constant determines the final level. The block. Often only one sensor is used by strategically locating a integrator time constant is programmable in 32 steps from 40s point where optimum signal output is available. The ability of to 600s. This time constant can be viewed as an output signal this IC to have programmable gain changes at each ignition attenuator. Again, the value of the time constant is set by the pulse can help with these configurations. In some high end SPI control signals from the microcontroller. applications two HIP9011 are used. Immediately after the INT/HOLD signal goes low, the The input coupling capacitor and series input resistors to the integrators output signal, INTOUT is held in the HIP9011s inverting input of the operational amplifiers within the HIP9011 output sample and hold circuit for the microcontrollers A/D serve as a high pass filter to reduce low frequency components converter to process. Figure 2 shows the block diagram of the from the transducer. AC coupling also has the advantage of HIP9011. Figure 3 shows the waveforms for the integrator, reducing the possibility of driving the output of the input INTOUT on the top trace. The center trace shows the input amplifier towards the positive supply with increased leakage signal from a simulated pressure transducer mounted on the resistance of the transducer or environment with time. Leakage cylinder. An expanded waveform of the simulated engine input resistance to ground will pull the inverting input of the signal during the integration period is shown in the circled operational amplifier to ground, thus forcing its output high. The display of Figure 3. The bottom trace shows the INT/HOLD non-inverting input of the HIP9011 is not committed, but in most signal. applications, it is usually returned to the mid supply voltage, available as an output terminal of the device. From this discussion we see that we have an IC that can detect low levels of engine knock or ping by using bandpass filters, A signal from the engines microcontroller determines which rectification and an integration process. The gated integrator transducer input signal will be processed by the HIP9011 allows the IC to only monitor engine noise during the time that operational amplifier for each ignition pulse by toggling the engine knock is expected to occur, thus, vastly reducing the transmission gate on the output of these amplifiers. From here influence of background noise. the signal is applied to an anti aliasing filter within the HIP9011. This filter excludes input signals above 20kHz from passing on Integrator Operation to the following switched capacitor filter and gain stages. Observation of the integrator output signal, INTOUT, is Signals above 20kHz could cause problems with the 200kHz important to the setup and understanding of the operation of clocking frequency of the switched capacitor filters and this signal processing IC. This observation can be distorted by amplifiers. A filter channel is provided in the HIP9011, with a instrumentation used to view the INTOUT signal. In Figure 5, tuning range from 1.22kHz to 19.98kHz, in 64 steps. Serial the upper waveform shows what looks like inaccuracies in the control signals are sent via the SPI bus to the HIP9011 by the INTOUT signal. This is due to aliasing of the oscilloscope microcontroller. These control signals set the filter frequencies sampling system with only 500 samples. Not shown in this within these ICs. AN9770 Rev 1.00 Page 2 of 15 Nov 6, 2006 CHANNEL SELECT SWITCHES 3RD ORDER ANTIALIASING FILTER