Integrated circuit with configurable on-die termination
Described are integrated-circuit die with differential receivers, the inputs of which are coupled to external signal pads. Termination legs coupled to the signal pads support multiple termination topologies. These termination legs can support adjustable impedances, capacitances, or both, which may be controlled using an integrated memory.
1. An integrated-circuit (IC) die programmable to support a first termination topology and a second termination topology, the IC die comprising:
an input pad to receive an input signal;
a receiver having an input terminal coupled to the input pad to receive the input signal, a reference terminal to receive a reference signal; and an output terminal to issue an output signal responsive to the input signal and the reference signal; and
first and second termination legs to support the first termination topology and the second termination topology, the first and second termination legs connecting the input terminal to a first-supply-voltage node and a second-supply-voltage node, respectively, in the first termination topology and coupling the input terminal to the reference terminal in the second terminal topology.
2. The IC die of claim 1 , the first termination leg including a first termination impedance and the second termination leg including a second termination impedance.
3. The IC die of claim 2 , wherein the first termination impedance and the second termination impedance each connect directly to the input terminal.
4. The IC die of claim 3 , further comprising a first switch to selectively connect the first termination impedance to the first-supply-voltage node and a second switch to selectively connect the second termination impedance to the second-supply-voltage node.
5. The IC die of claim 4 , further comprising a memory coupled to the first switch and to the second switch, the memory to store a value controlling the first switch and the second switch.
6. The IC die of claim 1 , wherein the reference terminal applies a reference voltage midway between a first voltage applied to the first-supply-voltage node and a second voltage applied to the second-supply-voltage node.
7. The IC die of claim 1 , wherein the second-supply-voltage node is at ground potential.
8. The IC die of claim 1 , further comprising a coupling switch and a capacitance coupled in parallel between the input pad and the input terminal, the coupling switch to selectively DC couple the input pad to the input terminal.
9. The IC die of claim 8 , further comprising a memory coupled to the coupling switch, the first termination leg, and the second termination leg, the memory to store values controlling the coupling switch, the termination leg, and the second termination leg.
10. The IC die of claim 1 , the first and second termination legs each further comprising a capacitor coupled in series between the input terminal and the respective one of the first-supply-voltage node and the second-supply-voltage node.
11. The IC die of claim 10 , the first and second termination legs each further comprising a switch coupled in parallel with the respective capacitor.
12. An integrated-circuit (IC) die programmable to support a filtered termination topology or an unfiltered termination topology, the IC die comprising:
an input pad to receive an input signal;
a receiver having an input terminal coupled to the input pad to receive the input signal, a reference terminal to receive a reference signal; and an output terminal to issue an output signal responsive to the input signal and the reference signal; and
first and second termination legs to support the filtered termination topology and the unfiltered termination topology, the first and second termination legs connecting the input terminal to a first filter node and a second filter node, respectively, in the filtered termination topology and connecting the input terminal to a reference node in the unfiltered termination topology.
13. The IC die of claim 12 , the first termination leg including a first termination impedance and the second termination leg including a second termination impedance.
14. The IC die of claim 13 , wherein the first termination impedance and the second termination impedance each connect directly to the input terminal.
15. The IC die of claim 14 , further comprising a first switch to selectively connect the first termination impedance to the first filter node and a second switch to selectively connect the second termination impedance to the second filter node.
16. The IC die of claim 15 , further comprising a memory coupled to the first switch and to the second switch, the memory to store a value controlling the first switch and the second switch.
17. The IC die of claim 12 , further comprising a first capacitor between the first filter node and the reference node and a second capacitor between the second filter node and the reference node.
18. The IC die of claim 12 , further comprising a memory coupled to the first and second termination legs, the memory storing a value to distinguish between the filtered termination topology and the unfiltered termination topology.
19. The IC die of claim 12 , each of the first and second termination legs including an adjustable on-die termination impedance.