Sense amplifier circuit, corresponding memory device and method of operation
First, second input terminals of a sense amplifier are coupled to first, second memory sensing nodes. A first input transistor has a channel arranged between a first comparator input and a first comparator output, and a control terminal at a bias node. A second input transistor has a channel arranged between a second comparator input and a second comparator output, and a control terminal at a bias node. The first and second comparator inputs are selectively couplable to each other, in response to compensation signal assertion, or to the first and second input terminals, in response to compensation signal de-assertion. The bias node is selectively couplable to a comparator biasing node in response to bias enable assertion, or is floating in response to the bias enable de-assertion. A sensing circuit produces a read signal as a function of a difference between first, second currents at the comparator outputs.
1 . A sense amplifier circuit for a memory device, comprising:
a first input terminal and a second input terminal configured for coupling to a first memory sensing node and a second memory sensing node, respectively;
a comparator circuit comprising:
a first input node and a second input node;
a first output node and a second output node configured to produce a first output current and a second output current, respectively;
a first input transistor having a conductive channel arranged between said first input node and said first output node of the comparator circuit, and a first control terminal coupled to an internal biasing node;
a second input transistor having a conductive channel arranged between said second input node and said second output node of the comparator circuit, and a second control terminal coupled to said internal biasing node;
wherein said first input node and said second input node of the comparator circuit are selectively couplable to each other in response to assertion of a compensation signal, and selectively couplable to said first and second input terminals, respectively, in response to de-assertion of said compensation signal;
wherein said internal biasing node is selectively couplable to a comparator biasing node in response to assertion of a bias enable signal, and selectively left floating in response to de-assertion of said bias enable signal;
a sensing circuit coupled to said first output node and to said second output node of the comparator circuit, said sensing circuit configured to produce a memory reading signal as a function of a difference between said first output current and said second output current.
2 . The sense amplifier circuit of claim 1 , wherein said first input transistor comprises a p-channel MOS transistor having a source terminal coupled to said first input node and a drain terminal configured for coupling to said first output node, and said second input transistor comprises a p-channel MOS transistor having a source terminal coupled to said second input node and a drain terminal configured for coupling to said second output node.
3 . The sense amplifier circuit of claim 1 , wherein said first input transistor and said second input transistor have a same size.
4 . The sense amplifier circuit of claim 1 , wherein a capacitive coupling between said internal biasing node and ground is negligible with respect to a capacitive coupling between said internal biasing node and said first and second input nodes of the comparator circuit.
5 . The sense amplifier circuit of claim 1 , wherein a capacitance between said internal biasing node and ground is at least ten times lower than a capacitance between said internal biasing node and said first and second input nodes of the comparator circuit.
6 . The sense amplifier circuit of claim 1 , wherein a capacitance between said internal biasing node and ground is at least twenty times lower than a capacitance between said internal biasing node and said first and second input nodes of the comparator circuit.
7 . The sense amplifier circuit of claim 1 , wherein a capacitance between said internal biasing node and ground is at least fifty times lower than a capacitance between said internal biasing node and said first and second input nodes of the comparator circuit.
8 . The sense amplifier circuit of claim 1 , wherein a capacitance between said internal biasing node and ground is at least one hundred times lower than a capacitance between said internal biasing node and said first and second input nodes of the comparator circuit.
9 . The sense amplifier circuit of claim 1 , wherein said comparator circuit comprises a first capacitor arranged between said internal biasing node and said first input node, and a second capacitor arranged between said internal biasing node and said second input node.
10 . The sense amplifier circuit of claim 1 , wherein said comparator circuit comprises:
a first cascode transistor having a conductive channel arranged in series with the conductive channel of said first input transistor, and a control terminal configured to receive a cascode enable signal; and
a second cascode transistor having a conductive channel arranged in series with the conductive channel of said second input transistor, and a control terminal configured to receive said cascode enable signal.
11 . The sense amplifier circuit of claim 1 , wherein said first input node and said second input node of the comparator circuit are further selectively couplable to a regulated supply node that provides a regulated supply voltage in response to assertion of said compensation signal.
12 . The sense amplifier circuit of claim 1 , wherein said sensing circuit comprises:
a first capacitor having a first terminal coupled to said first output node;
a first inverter having an input terminal coupled to a second terminal of said first capacitor and an output terminal coupled to said second output node;
a second capacitor having a first terminal coupled to said second output node;
a second inverter having an input terminal coupled to a second terminal of said second capacitor and an output terminal coupled to said first output node; and
a latch circuit configured to sense a differential voltage between said first and second output nodes and produce a digital sensing signal as a function thereof in response to assertion of a latch enable signal.
13 . A memory device, comprising:
a plurality of memory banks;
wherein:
each memory bank is coupled to a respective sense amplifier circuit according to claim 1 ; and
each memory bank comprises an array of memory cells arranged in a plurality of bit lines and a plurality of word lines, wherein each memory cell is arranged in series to a respective selection transistor between a ground terminal and a corresponding bit line of the plurality of bit lines, and wherein each bit line of the plurality of bit lines is couplable to: a regulated supply node that provides a regulated supply voltage or one of said first and second memory sensing nodes.
14 . The memory device of claim 13 , further comprising a biasing circuit coupled to said regulated supply node and configured to produce a comparator biasing voltage at said comparator biasing node.
15 . The memory device of claim 14 , wherein the biasing circuit comprises a first current flow line arranged between said regulated supply node and ground, the first current flow line comprising:
a first diode-connected transistor having a conductive channel arranged between said regulated supply node and an internal node;
a second transistor and a third diode-connected transistor having their conductive channels arranged in series between said regulated supply node and said internal node, wherein said second transistor has a same size as said first diode-connected transistor and is configured to receive a same control signal as said first diode-connected transistor;
a fourth diode-connected transistor having a conductive channel arranged between said internal node and a further internal node; and
a current generator arranged between said further internal node and ground, and configured to sink a current from said further internal node;
wherein the biasing circuit comprises a second current flow line arranged between said regulated supply node and ground, the second current flow line comprising:
a fifth transistor having a conductive channel arranged between said regulated supply node and said comparator biasing node, wherein said fifth transistor is configured to receive the same control signal as said third diode-connected transistor; and
a sixth transistor having a conductive channel arranged between said comparator biasing node and ground, wherein said sixth transistor is configured to receive the same control signal as said fourth diode-connected transistor;
wherein the biasing circuit preferably comprises a capacitor arranged between said regulated supply node and said comparator biasing node.
16 . The memory device of claim 15 , wherein said first diode-connected transistor and said second transistor have a same size as said first input transistor and said second input transistor of the comparator circuit.
17 . The memory device of claim 15 , further comprising an operating mode configured to:
i) assert the bias enable signal to couple said internal biasing node of said comparator circuit to said comparator biasing node, and assert said compensation signal to couple said first input node and said second input node to each other;
ii) couple at least one pair of selected bit lines to said regulated supply node to pre-charge said selected bit lines to a target voltage;
iii) upon expiration of said pre-charge of said pair of selected bit lines: decouple said pair of selected bit lines from said regulated supply node; couple said pair of selected bit lines to said first and second memory sensing nodes, respectively; de-assert said bias enable signal to make said internal biasing node of said comparator circuit float; and enable and equalize said sensing circuit;
iv) upon expiration of an equalization interval, de-assert said compensation signal to couple said first input node and said second input node to said first input terminal and to said second input terminal, respectively, and activate said sensing circuit; and
v) upon expiration of a sensing interval, produce said memory reading signal.