Apparatus having feedback loops between multiple pairs of instrumentation modules

1. A multichannel measurement apparatus, comprising:

a frame to accommodate more than two instrumentation modules;

a multiplexed bus associated with the frame, the bus comprising more than two connectors, each for connection to a respective instrumentation module; and

a sense instrumentation module and a source instrumentation module mounted in the frame and electrically connected to respective ones of the connectors, the sense instrumentation module and the source instrumentation module collectively comprising:

a circuit path comprising a sense circuit, a feedback controller, and a source circuit coupled in order in series between a sense input and a source output, the sense circuit to generate a sense output signal representing a sensed parameter dependent on a source signal, the feedback controller to generate a control signal in response to the sense output signal, the source circuit to generate the source signal in response to the control signal; and

a communication link in the circuit path, the communication link comprising a bus transmitter and a bus receiver each configured to select a channel of the multiplexed bus via which to communicate; in which:

the sense input, the sense circuit and the bus transmitter are parts of the sense instrumentation module; and

the bus receiver, the source circuit and the source output are parts of the source instrumentation module.

2. The apparatus of claim 1 , in which the communication link is between the sense circuit and the feedback controller.

3. The apparatus of claim 1 in which the communication link is between the feedback controller and the source circuit.

4. The apparatus of claim 1 , in which the communication link is between parts of the feedback controller.

5. The apparatus of claim 4 , in which:

the feedback controller comprises a summing circuit and a control circuit in series; and

the communication link is between the summing circuit and the control circuit.

6. The apparatus of claim 1 , in which the multiplexed bus comprises a time division multiplexed bus.

7. The apparatus of claim 6 , in which the multiplexed bus comprises:

an information signal path, a frame signal path and a clock signal path; and

a bus controller to impose a frame signal on the frame signal path and a clock signal on the clock signal path.

8. The apparatus of claim 1 , in which:

the multiplexed bus has a transmission latency;

the apparatus has a feedback bandwidth; and

the transmission latency is less than a reciprocal of the feedback bandwidth.

9. The apparatus of claim 1 , in which the multiplexed bus comprises a frequency division multiplexed bus.

10. The apparatus of claim 1 , in which the multiplexed bus comprises a code division multiplexed bus.

11. The apparatus of claim 1 , in which the feedback controller comprises a ramp generator.

12. The apparatus of claim 1 , in which:

the bus transmitter and bus receiver are each configured to select a first channel of the multiplexed bus via which to communicate; and

the apparatus additionally comprises additional instrumentation modules mounted in the frame and comprising an additional bus transmitter and an additional bus receiver each configured to select a second channel of the multiplexed bus via which to communicate.

13. The apparatus of claim 1 , in which:

the bus transmitter and the bus receiver are each configured to select a first channel of the multiplexed bus via which to communicate;

the source instrumentation module additionally comprises an additional bus receiver;

the apparatus additionally comprises an additional sense instrumentation module mounted in the frame and comprising an additional bus transmitter, the additional bus transmitter and the additional bus receiver configured to select a second channel of the multiplexed bus via which to communicate; and

the feedback controller is located in the source instrumentation module and comprises a signal processor and a control circuit, the signal processor to subject respective feedback signals received from the sense instrumentation module and from the additional sense instrumentation module to an arithmetic operation prior to input to the control circuit.

14. The apparatus of claim 1 , in which the sense instrumentation module and the source instrumentation module are fabricated on a common substrate.

15. The apparatus of claim 1 , in which the sense circuit is to generate the sense output signal from an instrument signal received from an external instrument, the instrument signal representing the parameter sensed by the external instrument.

16. The apparatus of claim 1 , additionally comprising a communication interface connected to the multiplexed bus.

17. The apparatus of claim 16 , additionally comprising one of an electrical, and optical, and a wireless communication path connected to the communication interface.

18. The apparatus of claim 1 , in which the source circuit is to generate, in response to the control signal, an instrument control signal for controlling generation of the source signal by an external source instrument.

19. A multichannel measurement system, comprising:

a multichannel measurement apparatus in accordance with claim 1 ,

a communication interface coupled to the multiplexed bus;

an external instrumentation module external to the multichannel measurement apparatus, the external instrumentation module linked to one of the source instrumentation module and the sense instrumentation module via the communication interface and a channel of the multiplexed bus.

20. The multichannel measurement system of claim 19 , in which the external instrumentation module is one of (a) an external sense instrumentation module to receive an instrument signal from an external instrument, the instrument signal representing a parameter sensed by the external instrument, and (b) an external source instrumentation module to output an instrument control signal to control generation of an external source signal by an external source instrument.