Provides the very high output impedance based on the instrument and operational amplifier’s traditional current supply and the voltage/commutator under low frequency, this is because the amplifier has good low frequency CMRR (syntype rejection ratio). Under the high frequency, CMRR which, the inherent output capacity, the transfer ratio limitation reduced has prevented high grade current supply realization. Analog Devices Corporation’s two section of 200 MHz line receive/enlarged IC–AD8129 and AD8130– has provided the differential input and remarkable CMRR, causes powerful candidate who they became the construction high frequency constant current. Figure 1 the electric circuit has provided the good beginning, but AD8130 high input bias current possibly when the electric current level will be low will affect the output current precision.
In order to overcome this question, may increase unit gain buffer IC2 to isolate the electric current sensing resistor (Figure 2). Moreover, may survey the load voltage and from lifts output cable’s electric capacity using the buffer amplifier. This electric circuit when 1MHz presents the output impedance approximately is 500k, and uses ±5V time the power source, the electric current standards scope is 0V to ±3V.
Has the capacitive coupling load current supply to profit in a cocurrent servo loop comes stabilizing circuit’s operating point (Figure 3). The output coupling capacitor CO value is decided by the request low frequency weaken characteristic. The basic electric circuit’s further improvement has realized output capacity’s compensation, and increased electric circuit’s output impedance. Small adjustable feedback capacitor CCOMP approximately for out-port’s stray capacity’s half, has provided the forward feed compensation, and further reduced out-port’s stray capacity’s influence (Figure 4). In order to prevent the vibration, electric cable’s shield driving circuit’s gain should slightly be lower than the unit gain. Attention: If drops to output current sensing resistor R9 100Ω, can compensate the input attenuator which is composed of R1 and R2, and maintains 1 mA/V characteristic. This voltage/current supply’s frequency range is 20Hz to 10 MHz. If must realize the optimum result, please use the high-frequency circuit layout and the power source bypass method.
