2.1 Introduction
The multi-level amplifier proposed in this dissertation provides greater flexibility and wider bandwidth than those that rely on high voltage op-amps.
The circuit is easily implemented by connecting floating signal modules in series. The general idea of multi-level amplifier is slightly similar to the circuit topology proposed by H. Ertl et al. [15] in 2002. These floating modules are realized using IC-style op-amps. When configured in this way, the multi-level amplifier can deliver output voltage swings that are the sums of the swings of individual modules. The conception of multi-level amplifier can be illustrated briefly in Fig. 2.1 and 2.2. Figure 2.1 shows a generic difference amplifier, where Vb denotes the reference potential of difference amplifier. In a general application, V is defined as the real ground of system and its value equals to b zero. Fig. 2.2(a) illustrates this case when V equals to zero, the output voltage b of difference amplifier is bounded approximately in the range of dual power supplies rail, where solid lines indicate the power supplies rail and dotted line is the output voltage. Therefore, if the reference potential V has an un-zero value b relative to real ground, then the output voltage of differential amplifier is the value of the summation of V and the pure output voltage relative to reference b potential Vb as shown in Fig. 2.2(b).
Hence, the amplifier topology applies an un-zero reference potential V is b named as “floating” module in this dissertation. As shown in Fig. 2.3, applying the conception of floating module, the ground reference in the first side and floating reference in the second side are detached from the isolation amplifier.
Such a floating module with difference amplifier is named as “Isolated Floating Difference Amplifier” and IFDA is used for its abbreviation in this dissertation.
And a module which consists of non-inverting configuration and inverting configuration isolated floating difference amplifiers is as shown in Fig. 2.4. It is named as “Balanced Floating Difference Amplifier” and BIFDA is used as its abbreviation.
The goal and idea of this study is to construct a circuit topology by utilizing the cascade of multiply floating modules to provide a large output signal and to own a high operational bandwidth. Each independent floating module, BIFDA, in the cascaded circuit topology is named as one level. As the overall gain is increased by adding floating signal modules, the bandwidth does not change.
The power dissipated by the amplifier increases with frequency because capacitors draw more current at higher frequencies. The output of each floating signal module can deliver the same current to the load. The maximum output power may be dissipated by each module. According to the conceptions illustrated above, two circuit topologies are proposed as direct-floating cascaded topology and indirect-floating cascaded topology as shown in Fig. 2.3(a) and Fig.
2.3(b). Following sections will describe both topologies in the detail.
2.2 Cascade Amplifier
According to the conceptions illustrated in section 2.1, how to create floating references for each BIFDA is the key point of the floating amplifier topology which is proposed in this dissertation. Figure 2.5(a) and (b) show two topologies to create and construct the floating amplifiers. Figure 2.5(a) is an indirect-floating cascaded module, where the floating references Vb of non-inverting configuration and inverting configuration in each BIFDA level are connected to each other, and output signal of non-inverting configuration in the ith level is connected to the output signal of inverting configuration in the (i+1)th level. The total output voltage of indirect-floating module is drained from the
non-inverting configuration of nth level into the inverting configuration of the first level. Figure 2.5(b) is direct-floating cascaded module, where the floating reference of non-inverting configuration V in the (i+1)b+ th level is supplied and maintained by the output voltage of non-inverting configuration Vout,p in the ith level; the floating reference of inverting configuration V in the (i+1)b− th level is supplied and maintained by the output voltage of inverting configuration Vout,n in the ith level. The total output voltage of direct-floating module is drained between the non-inverting and inverting configuration of nth level.
Figure 2.6(a) and (b) show the gain principle of multi-level balanced isolated floating difference amplifier, which is abbreviated as MBIFDA, in both indirect- and direct-floating cascaded topologies. The indirect-floating cascaded topology as shown in Fig. 2.6(a), each difference amplifier has the same amplified value of G, and a floating reference 'F exists in the ith level and F "
is in the (i+1)th level. As mentioned above, the output signal of non-inverting configuration in the ith level is connected to the output signal of inverting configuration in the (i+1)th level.
"
' G F
F
G+ =− + (2.1)
G F
F"= '+2 (2.2)
Hence, the system output signal of indirect-floating cascaded topology can be derived as
G F G G F G F
G F
G
Vout = + "−(− + ')= +( '+2 )+ − '=4 (2.3) The output voltage derivation of MBIFDA in an n level system can analogous with Eq. (2.3) as 2nG. Compared with Fig. 2.6(a), the direct-floating cascaded topology as shown in Fig. 2.6(b) has differences of a floating reference 'F exists in the non-inverting configuration and "F is in the inverting configuration of the ith level. Hence the system output signal drains from the (i+1)th BIFDA is
"
' 4
)
"
2 ( ) ' 2
( G F G F G F F
Vout = + − − + = + − (2.4),
where the floating reference 'F and "F are not equal to each other. But referring to Fig. 2.5(b), in the first level of direct-floating cascaded MBIFDA, the reference voltages of non-inverting and inverting configuration are identical.
Hence, the output voltage derived from direct-floating cascaded MBIFDA is eventually equal to the result of the indirect one, Vout =2nG.
In chapter 3, the indirect-floating cascaded topology will be introduced and analyzed in the detail, and chapter 4 presents the direct-floating cascaded topology.