Analog to digital conversion with charge balanced voltage to frequency converter having polarity responsive offset
First Claim
1. A circuit for converting an input voltage having first and second opposite polarities to an output frequency wherein the output frequency is related to the value of the input voltage, the input voltage value including zero, the output frequency having a non-zero value for a zero input value, comprisinga capacitor;
- means responsive to the input voltage for cyclically charging the capacitor in first and second opposite directions so that zero net charge is applied to the capacitor during each cycle, the means for charging including means for charging the capacitor (a) in the first direction at a first rate determined by the value of the input voltage and a predetermined current while the input voltage has the first polarity, (b) in the second direction at a second rate determined by the value of the input voltage while the input voltage has the first polarity, (c) in the first direction at a third rate determined by the value of the input voltage, a predetermined voltage and the predetermined current while the input voltage has the second polarity and (d) in the second direction at a fourth rate determined by the value of the input voltage, the predetermined voltage while the input voltage has the second polarity, the predetermined voltage and predetermined current being of opposite polarity; and
means responsive to the charging and discharging of the capacitor for deriving the output frequency.
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Accused Products
Abstract
A bipolar analog voltage is converted into a digital signal by sensing the polarity of the voltage and selectively supplying a bias voltage to an analog-to-digital converter, which can preferably be a charge balanced voltage to frequency converter, as a function of the sensed polarity. The voltage to frequency converter has a double valued variable frequency output with a discontinuity at zero volt such that the converter derives a maximum output frequency for a maximum positive voltage and also for a negative value slightly displaced from zero; the voltage to the frequency converter minimum output frequency is derived from positive voltages slightly greater than zero and for maximum negative voltages. The converter output frequency and the sensed polarity are supplied to a frequency to digital converter which derives an output signal having a bit representing the polarity of the analog voltage and additional bits indicative of the magnitude of the analog voltage.
14 Citations
13 Claims
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1. A circuit for converting an input voltage having first and second opposite polarities to an output frequency wherein the output frequency is related to the value of the input voltage, the input voltage value including zero, the output frequency having a non-zero value for a zero input value, comprising
a capacitor; -
means responsive to the input voltage for cyclically charging the capacitor in first and second opposite directions so that zero net charge is applied to the capacitor during each cycle, the means for charging including means for charging the capacitor (a) in the first direction at a first rate determined by the value of the input voltage and a predetermined current while the input voltage has the first polarity, (b) in the second direction at a second rate determined by the value of the input voltage while the input voltage has the first polarity, (c) in the first direction at a third rate determined by the value of the input voltage, a predetermined voltage and the predetermined current while the input voltage has the second polarity and (d) in the second direction at a fourth rate determined by the value of the input voltage, the predetermined voltage while the input voltage has the second polarity, the predetermined voltage and predetermined current being of opposite polarity; and means responsive to the charging and discharging of the capacitor for deriving the output frequency. - View Dependent Claims (2, 3)
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4. A circuit for converting an input voltage having first and second opposite polarities to an output frequency wherein the output frequency is related to the value of the input voltage, the input voltage value including zero, the output frequency having a non-zero value for a zero input voltage value, comprising a charge balanced voltage to frequency converter responsive to the input voltage, and means responsive to the input voltage having the first and second polarities for supplying a predetermined bias voltage having the first polarity only when the input voltage is at the second polarity.
- 5. An analog to digital converter responsive to an input voltage source having first and second polarities and a predetermined amplitude range, comprising means for converting the input voltage into an output frequency, the output frequency varying as a function of the amplitude and polarity of the input voltage such that there is a step function change in the output frequency with changes in polarity of the input voltage, the output frequency having the same value for two different magnitudes and polarities of the input voltage, and means responsive to the polarity of the input voltage and the output frequency for deriving a digital signal having different values for different voltages throughout the range.
- 10. Apparatus for converting a bipolar analog input voltage into a digital signal, comprising a polarity sensor responsive to the analog input voltage, a voltage-to-frequency converter responsive to the polarity sensed by the polarity sensor and the analog input signal for deriving a variable frequency signal having double values of frequency as a function of the magnitude of the analog input signal and its polarity and a discontinuity in the frequency derived thereby as the analog input signal changes polarity, a frequency-to-digital converter responsive to the variable frequency output of the voltage-to-frequency converter and of the polarity sensor for deriving a digital signal having a polarity bit indicative of the sensed polarity and additional bits controlled by the frequency derived by the voltage-to-frequency converter and the sensed polarity.
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13. A circuit for converting an input voltage having first and second opposite polarities to a digital representation of the input voltage, the input voltage having positive and negative values as well as zero, the digital representation being double valued such that (a) said representation increases from a low value to a high value as the input voltage of the first polarity increases from zero to a full scale value, (b) the digital representation decreases from said high value to said low value as the input voltage of the second polarity increases from zero to said full scale value and (c) a polarity signal is generated indicating which state (a) or (b) applies, said circuit comprising:
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means for converting input voltages of the first polarity to corresponding digital representations; a plurality of sensing elements responsive to said input voltage for generating said polarity signal; a source of a bias voltage equal to said full scale input voltage of the first polarity; and means for summing (1) a signal derived from the bias voltage with (2) a signal derived from the input voltage, when the input voltage is of the second polarity.
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Specification