junctions to the supplies because they are constructed from either p-or n-type diffusion regions. The substrate potential of the amplifier is the most critica component, for it will determine the sensitivity of an amplifiers input current voltage characteristic to supply voltage The configuration of the amplifiers input stage also plays a large role in the curren voltage characteristic of the amplifier Input differential pairs of operationa amplifiers are constructed from either bipolar transistors(NPN or PNP)or field- effect transistors junction or MOs, N-or P-channel). While the bipolar input differential pairs do not have any direct path to either supply, fet differential pairs do. For example, an n-channel JFET forms a parasitic p-n junction between its backgate and the psubstrate that energizes when Vin+0.7V< VNEG As mentioned previously, many manufacturers of analog integrated circuits do not provide any details with regard to the behavior of the device's input structure Either simplified schematics are not provided or, if they are shown, the behavior of the input stage under an overvoltage condition is omitted Therefore, other measures must be taken in order to identify the conduction paths a standard transistor curve tracer can be configured to determine the current voltage characteristic of any amplifier regardless of input circuit topology As showr in Figure 7.2, both amplifier supply pins are connected to ground, and the collector output drive is connected to one of the amplifiers inputs. The curve tracer applies a DC ramp voltage and measures the current flowing through the input stage. In the event that a transistor curve tracer is not available, a dc voltage source and a multimeter can be substituted for the curve tracer. A 10kohm resistor should be used between the dC voltage source and the amplifier input for additional protection. Ammeter readings from the multimeter at each applied dC voltage will yield the same result as that produced by the curve tracer. Although either input can be tested(both inputs should), it is recommended that the unused input is left open; otherwise, additional junctions could come into play and would complicate matters further Evaluations of current feedback amplifier input stages are more difficult because of the lack of symmetry between the inputs. As a result, both inputs should be characterized for their individual current-voltage characteristics4 junctions to the supplies because they are constructed from either p- or n-type diffusion regions. The substrate potential of the amplifier is the most critical component, for it will determine the sensitivity of an amplifier’s input current￾voltage characteristic to supply voltage. The configuration of the amplifier’s input stage also plays a large role in the current￾voltage characteristic of the amplifier. Input differential pairs of operational amplifiers are constructed from either bipolar transistors (NPN or PNP) or field￾effect transistors (junction or MOS, N- or P-channel). While the bipolar input differential pairs do not have any direct path to either supply, FET differential pairs do. For example, an n-channel JFET forms a parasitic p-n junction between its backgate and the p-substrate that energizes when VIN + 0.7V < VNEG. As mentioned previously, many manufacturers of analog integrated circuits do not provide any details with regard to the behavior of the device’s input structure. Either simplified schematics are not provided or, if they are shown, the behavior of the input stage under an overvoltage condition is omitted. Therefore, other measures must be taken in order to identify the conduction paths. A standard transistor curve tracer can be configured to determine the current￾voltage characteristic of any amplifier regardless of input circuit topology. As shown in Figure 7.2, both amplifier supply pins are connected to ground, and the collector output drive is connected to one of the amplifier’s inputs. The curve tracer applies a DC ramp voltage and measures the current flowing through the input stage. In the event that a transistor curve tracer is not available, a DC voltage source and a multimeter can be substituted for the curve tracer. A 10kohm resistor should be used between the DC voltage source and the amplifier input for additional protection. Ammeter readings from the multimeter at each applied DC voltage will yield the same result as that produced by the curve tracer. Although either input can be tested (both inputs should), it is recommended that the unused input is left open; otherwise, additional junctions could come into play and would complicate matters further. Evaluations of current feedback amplifier input stages are more difficult because of the lack of symmetry between the inputs. As a result, both inputs should be characterized for their individual current-voltage characteristics