Sampling and analog-to-digital converter apparatus for use in a telephone message metering system

Claim 2

In a message metering system for metering the usage of a plurality of subscriber units in a telephone system, the apparatus comprising, metering line means for carrying multi-level signals, one signal for each of a plurality of subscriber units in the telephone system, attenuator means connectEd to receive said multi-level signals for forming multi-level attenuated signals where said attenuated signals include a plurality of levels representing usage conditions, analog gate means for sampling said attenuated signals to form sampled signals, analog-to-digital converter means for converting said sampled signals to digital representations.

Claim 3

The apparatus of claim 1 wherein said analog gate means includes pairs of diodes where the diodes for each of said pairs are connected in series in opposite conduction directions and includes selection means for biasing said pairs of diodes on or off where each pair transmits the voltage level of a sampled signal when biased on.

Claim 4

The apparatus of claim 2 wherein said analog gate means further includes a field effect transistor selection gate having multiple inputs connected to receive the sampled signals from said pairs of diodes and operative to selectively provide an input to said converter means.

Claim 5

The apparatus of claim 3 further including address decode means for selecting one of said pairs of diodes and for separately selecting an associated one of said multiple inputs whereby a sampled signal is input to said converter whenever said one of said pairs of diodes and said one of said multiple inputs are simultaneously selected.

Claim 6

The apparatus of claim 3 wherein said attenuator means includes an input resistor RB connected on one side to receive one of said multi-level signals and connected on the other side in series with a resistor RC which in turn is connected to a sink wherein said analog gate means receives an attenuated input signal from the point between said resistor RB and RC, whereby said input signal is said one of said multi-level signals attenuated by a linear transformation proportional to the ratio of RC to the sum of RC and RB.

Claim 7

The apparatus of claim 5 wherein said attenuator means further includes a diode D3 series connected to a resistor RD and together connected in parallel with said resistor RB whereby the voltage transformation of said attenuator means is unchanged when said diode D3 is reverse biased and is proportional to the ratio of RC to the sum of RC and the parallel combination of RD and RB when said diode D3 is forward biased.

Claim 8

The apparatus of claim 5 wherein said attenuator further includes a capacitor C1 connected from a point between said resistors RB and RC to ground whereby said capacitor is operative to store the voltage across said resistor RC and is operative to discharge said voltage whenever said analog gate means is in a conduction state whereby the current through said resistor RC is not altered as a function of the conduction state of said analog gate means.

Claim 9

The apparatus of claim 5 wherein said attenuator means further includes a current source connected to said metering line means for providing current into said metering line means whenever said metering line means appears as a resistive network thereby providing one of said multi-level signals to said attenuator means.

Claim 10

The apparatus of claim 7 including a bias of a first polarity connected to one of said multiple inputs on one side of said analog gate means and a bias of an opposite polarity on the other side of said analog gate means whereby an associated one of said pairs of diodes is cut-off whenever said one of said multiple inputs is open thereby preventing discharge of said capacitor except when said one of said multiple inputs and said associated one of said pairs of diodes are simultaneously selected in the conduction state.

Claim 11

The apparatus of claim 5 further including means for selectively establishing said sink at different voltage levels whereby said attenuator means is selected to operate in a normal mode or in a test mode.

Claim 12

The apparatus of claim 10 wherein said voltage levels are ground for normal mode, positive for testing said analog gate means in one state, and negative for testing said analog gate mEans in the opposite state.

Claim 13

The apparatus of claim 1 wherein said analog-to-digital converter comprises a plurality of comparators for detecting when the analog levels of said sampled signals exceed predetermined threshold levels and means for forming digital encoded values of the outputs from said comparators.

Claim 14

The apparatus of claim 12 further including a transmitter-receiver combination including a light-emitting diode connected to receive an output from said converter.

Claim 15

The apparatus of claim 13 further including a digital integrator for digitally integrating said digital encoded values to form reliable indications of said multi-level signals.

Claim 16

The apparatus of claim 1 further including a transmitter-receiver combination having a differential circuit for rejecting common mode voltages.

Claim 17

The apparatus of claim 15 wherein said differential circuit includes means for transmitting the DC signal level.

Claim 18

The apparatus of claim 16 wherein said differential circuit includes a light-emitting diode and a light-sensitive transistor.

Claim 19

In a message system for metering the usage of a plurality of subscriber units in a telephone system wherein each of a plurality of subscriber units is associated with a multilevel signal, the apparatus comprising, a plurality of metering lines for carrying the multi-level signals, one signal for each of a plurality of subscriber units in the telephone system, an attenuator for each of said subscriber units coupled to receive a multi-level signal from a corresponding subscriber metering line to form an attenuated multi-level signal, analog gate means, one for each of said attenuators, for sampling corresponding attenuated multi-level signals to form sampled signals, analog-to-digital converter means associated with a plurality of subscriber metering lines, for converting said sampled signals to digital representations, and means for addressing said analog gate means for selecting one gate means at a time as an input to said converter means.

Claim 20

In a message system for metering the usage of a plurality of subscriber units in a telephone system wherein each of a plurality of subscriber units is associated with a multilevel signal, the apparatus comprising, a plurality of metering lines for carrying the multi-level signals, one signal for each of a plurality of subscriber units in the telephone system, an attenuator for each of said subscriber units coupled to receive a multi-level signal from a corresponding subscriber metering line to form an attenuated multi-level signal, analog gate means, one for each of said attenuators, for sampling corresponding attenuated multi-level signals to form sampled signals, analog-to-digital converter means associated with a plurality of subscriber metering lines, for converting said sampled signals to digital representations, and means for addressing said analog gate means for selecting one gate means at a time as an input to said converter means.