Parallel analog-digital converter with dual static ladder
The invention relates to fast, high resolution, analog digital converters, and more particularly those which possess at least one conversion stage of “flash” type. The converter according to the invention uses N differential amplifiers with four inputs. The amplifier of rank j receives the input voltage to be converted V ep −V en on two first inputs, and a reference potential difference on two other inputs. The reference potential difference is obtained between two taps of networks of resistors that are identical operating in parallel and supplied between a high voltage source and a low current source; the taps for an amplifier are respectively a tap P j of rank j of a first network and a tap P′ N−j+1 of rank N−j+1 of a second network. This reduces the first and second order non-linearity effects due to the fact that the differential amplifiers consume an input current tapped off from the networks of resistors.
1. An analog-digital converter comprising a network of N differential amplifiers of rank j=1 to N, each having four inputs, two inputs receiving a differential input voltage to be converted V ep −V en , the third and the fourth inputs receiving reference voltages arising from a set of resistors of identical nominal values R traversed by a current of nominal value I 0 , the amplifier of rank j providing a voltage proportional to V ep −V en −K·R·I 0 when the differential input voltage V ep −V en is close to a voltage value K·R·I 0 ,
wherein
the set of resistors comprises
a first network of N resistors of value R in series connected on one side to a constant voltage source and on the other to a constant reference current source, the ends of the resistors defining N first taps of rank j=1 to N, and
a second network of N resistors of value R in series connected on one side to the said constant voltage source and on the other to another constant reference current source or the constant reference current source such that the two networks are supplied by identical currents, the resistors of the second network defining N second taps of rank j=1 to N, and
the amplifier of rank j having its third input linked to a tap of rank j of the first network and its fourth input linked to a tap of rank N−j+1 of the second network, and
each of the networks of resistors has a configuration in which each resistor is formed of two resistors in parallel, placed symmetrically with respect to the middle of the network.
2. The converter as claimed in claim 1 , wherein a respective current source of value I 0 is provided in series with each network to impose the current which will traverse them.
3. The converter as claimed in claim 1 , wherein a current source of value 2I 0 is designed to supply the set of the two networks, each of them then being essentially traversed by half the current, namely a current I 0 .
4. The converter as claimed in claim 1 , producing N useful output voltages on conversion, comprising a number of amplifiers and resistors greater than N, the additional amplifiers and resistors being present solely to avoid edge effects.
5. The converter as claimed in claim 1 , wherein a decoupling capacitor is connected between each tap of the network and a terminal at fixed potential.
6. The converter as claimed in claim 2 , wherein a current source of value 2I 0 is designed to supply the set of the two networks, each of them then being essentially traversed by half the current, namely a current I 0 .
7. The converter as claimed in claim 2 , producing N useful output voltages on conversion, comprising a number of amplifiers and resistors greater than N, the additional amplifiers and resistors being present solely to avoid edge effects.
8. The converter as claimed in claim 3 , producing N useful output voltages on conversion, comprising a number of amplifiers and resistors greater than N, the additional amplifiers and resistors being present solely to avoid edge effects.
9. The converter as claimed in claim 2 , wherein each of the networks of resistors has a configuration in which each resistor is formed of two resistors in parallel, placed symmetrically with respect to the middle of the network.
10. The converter as claimed in claim 3 , wherein each of the networks of resistors has a configuration in which each resistor is formed of two resistors in parallel, placed symmetrically with respect to the middle of the network.
11. The converter as claimed in claim 2 , wherein a decoupling capacitor is connected between each tap of the network and a terminal at fixed potential.
12. The converter as claimed in claim 3 , wherein a decoupling capacitor is connected between each tap of the network and a terminal at fixed potential.
13. An analog-digital converter comprising:
a first network of resistors having N resistors in series coupled on one side to a voltage source and on the other to a first reference current source, the resistors of the first network of resistors defining N first taps of rank j=1 to N, and each resistor having resistance of a predetermined value R and being supplied with current of a predetermined value I 0 ;
a second network of resistors having N resistors in series coupled on one side to the voltage source and on the other to a second reference current source, the resistors of the second network of resistors defining N second taps of rank j=1 to N, and each resistor having resistance of the predetermined value R and being supplied with current of the predetermined value I 0 , the first and second reference current sources being arranged for supplying the first and second networks of resistors with identical amount of current; and
a network of amplifiers having N differential amplifiers of rank j=1 to N, each amplifier being configured to receive a pair of input signals V ep and V en and to provide an output signal responsive to V ep −V en −K·R·I 0 , K being N−2j+1, and having four inputs:
a first and second inputs of the four inputs being arranged for receiving the pair of input signals V ep and V en ,
a third input of the amplifier of rank j being connected to a tap of rank j of the first network of resistors, and
a fourth input of the amplifier of rank j being connected to a tap of rank N−j+1 of the second network of resistors,
wherein each of the networks of resistors has a configuration in which each resistor is formed of two resistors in parallel, placed symmetrically with respect to the middle of the network.
14. An analog-digital converter comprising:
a first network of resistors having N resistors in series coupled on one side to a voltage source and on the other to a reference current source, the resistors of the first network of resistors defining N first taps of rank j=1 to N, and each resistor having resistance of a predetermined value R and being supplied with current of a predetermined value I 0 ;
a second network of resistors having N resistors in series coupled on one side to the voltage source and on the other to the reference current source, the resistors of the second network of resistors defining N second taps of rank j=1 to N, and each resistor having resistance of the predetermined value R and being supplied with current of the predetermined value I 0 , the reference current source being arranged for supplying the first and second networks of resistors with identical amount of current; and
a network of amplifiers having N differential amplifiers of rank j=1 to N, each amplifier being configured to receive a pair of input signals V ep and V en and to provide an output signal responsive to V ep −V en −K·R·I 0 , K being N−2j+1, and having four inputs:
a first and second inputs of the four inputs being arranged for receiving the pair of input signals V ep and V en ,
a third input of the amplifier of rank j being connected to a tap of rank j of the first network of resistors, and
a fourth input of the amplifier of rank j being connected to a tap of rank N−j+1 of the second network of resistors,
wherein each of the networks of resistors has a configuration in which each resistor is formed of two resistors in parallel, placed symmetrically with respect to the middle of the network.