Filter with hysteresis for trip point applications

A circuit for processing a measurement signal indicative of a vehicle parameter, indicating if the vehicle parameter is below a first desired level or above a second desired level, comprising:

• means for providing first and second reference signals alternately selected in response to a control signal, the first reference signal selected if the control signal is a first signal condition and the second reference signal selected if the control signal is a second signal condition, the first reference signal being above the second reference signal;
• means for providing third and fourth reference signals alternately selected in response to the control signal, the fourth reference signal selected if the control signal is the first signal condition and the third reference signal selected if the control signal is the second signal condition, the third reference signal being above the fourth reference signal, the first and second reference signals being above the third reference signal;
• means for comparing the measurement signal to the selected reference signals and for providing a comparison output signal therefrom, wherein (i) if the first and fourth reference signals are selected, the comparison output signal has a first state if the measurement signal is below the first reference signal and above the fourth reference signal and a second state if the measurement signal is above the first reference signal or below the fourth reference signal, and (ii) if the second and third reference signals are selected, the comparison output signal has the first state if the measurement signal is below the second reference signal and above the third reference signal and the second state if the measurement signal is above the second reference signal or below the third reference signal;
• means for filtering the comparison output signal, including an up/down counter having overflow and underflow outputs providing overflow and underflow output signals as a filtered response to the comparison signal;
• means for providing the control signal in response to the overflow and underflow output signals, the control signal comprising the first signal condition if the comparison output signal has the second state for a predetermined number of clock pulses and the control signal comprising the second signal condition if the comparison output signal has the first state for a predetermined number of clock pulses, whereby the control signal is filtered and has hysteresis minimizing repeated switching of the control signal between the first and second signal conditions when the measurement signal is near one of the selected reference levels;
• means for alerting an operator in response to the control signal.

An apparatus for trip point application, comprising:

• means for receiving an input signal, means for comparing the input signal to a selected signal and means for providing a comparison signal in response to the comparison, the comparison signal having either a first or second state, the selected signal being either a first or a second reference signal, the first reference signal being higher than the second reference signal, the comparison signal having the first stage if the input signal is higher than the selected signal and the second state if the input signal is lower than the selected signal;
• an up/down counter selectively counting in a first direction if the comparison signal is the first state and selectively counting in a second direction if the comparison signal is the second state, the up/down counter having overflow and underflow outputs providing overflow and underflow output signals therefrom;
• and
• a multiplexer for selecting one of the reference signals in response to the overflow output signal and selecting the other reference signal in response to the underflow output signal, whereby, by selecting between the first and second reference signals, the apparatus filers with hysteresis;
• and
• means for signaling responsive to the overflow and underflow outputs of the multiplexer.

An apparatus for trip point applications, comprising:

• first comparing means for first comparing an input signal to a first selected signal and for controlling a state of a comparison signal responsive to the first comparison, the comparison signal having either a first or second state, the first selected signal being either a first or a second reference signal, the first reference signal being higher than the second reference signal;
• second comparing means for second comparing the input signal to a second selected signal and for controlling the state of the comparison signal responsive to the second comparison, the second selected signal being either a third or a fourth reference signal, the third reference signal being higher than the fourth reference signal and the second reference signal being higher than the third reference signal, the comparison signal having the first state if the input signal is higher than the first selected signal or lower than the second selected signal and the comparison signal having the second state if the input signal is lower than the first selected signal and higher than the second selected signal;
• an up/down counter selectively counting in a first direction if the comparison signal is the first state and selectively counting in a second direction if the comparison signal is the second state, the up/down counter having two counter outputs, providing two counter output signals therefrom;
• and
• multiplexer means for selecting the first and fourth reference signals as the first and second selected signals in response to one of the counter output signals of the up/down counter and for selecting the second and third reference signals as the first and second selected signals in response to the other of the counter output signals of the up/down counter, whereby, by selecting between the reference signals, the apparatus filters with hysteresis;
• and
• means for signaling an operator responsive to the counter outputs of the multiplexer means.

An integrated circuit apparatus for processing a set of measurement signals responsive to a set of senders, comprising:

• means for providing a set of reference signals, the set of reference signals comprising subsets of first and second reference signals, each subset corresponding to one of the measurement signals;
• memory means for addressably storing information, including an address input and a data output, wherein each reference signal of the set of reference signals corresponds to one address of a set of addresses in the memory means;
• counter means for selectively addressing the memory means, thereby selecting one of the subsets of reference signals;
• a set of filter means for filtering data, each filter means corresponding to one measurement of the set of measurement signals and one subset of reference signals, comprising:
• (i) means for addressing the memory means in response to a control signal to select the corresponding first or second reference signal;
• (ii) means for comparing a corresponding measurement signal to the selected reference signal and for providing a comparison output signal therefrom;
• (iii) means for filtering the comparison output signal, including an up/down counter having overflow and underflow outputs providing overflow and underflow output signals as a filtered response to the comparison output signal;
• (iv) means for providing the control signal in response to the overflow and underflow output signals, the control signal comprising a first signal condition fi the corresponding output signal is below the selected reference signal for a predetermined number of clock pulses and the control signal comprising a second signal condition if the corresponding output signal is above the selected reference signal for a predetermined number of clock pulses;
• wherein the counter means selectively activates each of the filter means so that only one filter means is activated at one time and the counter means selects the corresponding subset of first and second reference signals for each filter means, and
• wherein, the memory means is addressed in response to the control signal, thereby selecting the first or second reference signals.