扩展电流反馈放大器的可用性(5)

晶闸管电源

Texas Instruments IncorporatedAmplifiers: Op Amps

exactly the same as before. Figures 8 and 9 show the testcircuits for this configuration. The signal gain was kept ata gain of 5.

The same concepts apply for this CFB configuration asfor the noninverting configuration. The advantage of thiscircuit is that the attenuation is not limited to unity gain,or 0 dB, like the noninverting gain circuit. Figure 10 showsthe frequency responses of this configuration with varyingpure resistor values for Z. The THS4012 response is shownfor comparison purposes.

As expected, the responses all look comparable to eachother below 10 MHz. Additionally, the resistance valuesaffect the stability and again show that the higher theresistance is, the better the stability. Using a resistance aslow as 475 actually shows respectable performance in thisconfiguration. Remember that for oscillations to occur, thegain must be above unity gain, or 0 dB. As long as the peakis below 0 dB, oscillations should not occur. As in the non-inverting case, using 200 shows a large narrow peak thatwill most likely result in stability issues and/or oscillations.However, notice that above 10 MHz the same generalshape occurs for both the CFB and VFB amplifiers. This iscaused by the amplifiers’ input and output impedancesbecoming very high above their bandwidth limit. Whenthis occurs, there is a path for the input signal to flowthrough RG, through CF, and then to feed forward to theload. Of course, the amplifiers’ own input and output

capacitances also affect the amount of feed-through in thecircuit; but it is important to remember that this occursabove the amplifiers’ usable bandwidths.

Just as for the noninverting configuration, using ferritechips has several advantages for the inverting configuration.