CHAPTER 3 A Novel Bi-Directional Amplifier with Gain Control
3.6 Measurement Considerations
The reflection-type amplifier is a device with only one port to play the roles of the input and output ends. Therefore, a 2.4GHz circulator circuit has to be placed on the input port when the reflection-type amplifiers are measured alone. Otherwise, the gain and noise figure are unable to be measured because the reflected signal mixes with the incident signal. The measured methods of the reflection-type amplifier are similar to these of the bi-directional amplifier described below. The architecture is exhibited in Fig.3.22.
The reflection-type amplifiers connect with the branch-line circuit on FR4 board by means of bond wires so as to form the bi-directional amplifier. Utilizing the vector network analyzer HP8510C, the gain S21 and the return loss S11 can be measured. Also, the oscillatory situation will be estimated by observing the spectrum across the overall operating scope. In relation to the noise figure, the noise figure meter of Agilent HP8970B is adopted to measure this parameter. In regard to the 1-dB compression point, the different power levels will be inputted into the tested devices. Observing the output power levels, this point can be obtained. The diagram of testing procedure is presented in Fig.3.22.
Fig.3.1 (a) Passive Van Atta retro Fig.3.1 (b) Active Van Atta retro directive directive array Array with unilateral amplifier
Fig.3.1(c) Active Van Atta retro directive Array with bi-directional amplifier
Fig.3.2 The framework of a novel bi-directional amplifier
Fig.3.3 The configuration of negative resistance reflection-type amplifier
Fig.3.4 The input impedance of this amplifier
Fig.3.5 The framework of this reflection-type amplifier with gain control
Fig.3.6 The MOS model with source and drain load
Fig.3.7 The MOS noise model
Stable Region
Unstable Region
Fig.3.9 The gain of this reflection-type amplifier
Fig.3.10 The noise figure of this reflection-type amplifier
2.0 2.5 3.0
Fig.3.11 The input impedance changes as the value of the varied capacitance
m1freq=2.400GHz
Fig.3.12 The gain of this reflection-type amplifier changes with the value of the varied capacitance
Vcont=1.5v
Vcont=0v
Fig.3.13 The gain and noise figure of this reflection-type amplifier varies with the control voltage Vcont
Fig.3.14 The transmission line’s model of impedance transformation
Fig.3.15 The architecture of this hybrid
Fig.3.16 (a) The S parameters of this Branch-Line circuit
Fig.3.16 (b) The phase of this Branch-Line circuit
Fig.3.16 (c) The input impedance of this Branch-Line circuit
Fig.3.17 Photograph of the fabricated branch-line circuit
Fig.3.18 (b) The experimental phase response of this Branch-Line circuit
Fig.3.19 The gain and return loss of this bi-directional amplifier vary with the control voltage
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Fig.3.20 The spectrum across DC to 5 GHz
m2freq=2.4GHz
Fig.3.21 The noise figure of this amplifier varies with the controlled voltage Vcont=0v
Vcont=2v
Fig.3.22 The diagram of testing procedure
Fig.3.23 The layout of the two reflection-type amplifier 1102.6 um
992.7 um
Vcont2 Vin2
Gnd
Gnd Gnd
Vdd1
Vdd2
Gnd Vin1
Vcont1
TT FF SS F/S
Gain(dB) 13.6 13.9 12.5 13.6
P-1dB(dBm) -5.6 -4.4 -4.8 -5.6
NF 4.1 4.0 4.1 4.0
Table3.1 The parameters of this reflection-type amplifier vary in all kinds of the TSMC process
Design characteristic Freq-Range
(GHz) Gain S21 (dB) Return Loss S11 (dB)
2 ~ 18 0 ~ 4.5 12 ~ 30 accomplish amplifiers by
SPDT switches [21] 6 ~ 18 0 ~ 12 12 ~ 30
42 6 10 Common-gate type by
Modifying bias [20] 40 10 8
Novel bi-directional
amplifier [18] 6 9 6
This work 2.4 7.5 ~ 16 9.7 ~ 24
Table3.2 The specifications of this bi-directional amplifier compare with these of others
specification whole result result(1) result(2) Id(mA) 21
Centra1 frequency
(GHz) 2.4
P-1dB(dBm) -5~3 3 -5
Gain S21(dB) 7.5~16 7.5 16 Return Loss S11(dB) 9.7~24 24 9.7
Noise figure 4.1~5.4 5.4 4.1 Bandwidth(MHz) 150~220 220 150 Control voltage (V)
0~2 V 0 V 2 VPower dissipation(mA) 52*2
Chip size(um
2) 1102.6 x 992.7
Table3.3 The expected specifications of the bi-directional amplifier
CHAPTER 4 CONCLUSIONS
In the first section of this thesis, A Ka-Band Power Amplifier for Automotive Radar System is analyzed and designed. This circuit utilizes the semiconductor process of 0.15um GaInAs pHEMT power device to accomplish. In order to acquire the adequate linearity and efficiency of the system requirements, the architecture with two stages is adopted to design the power amplifier. The first stage utilizes class-A type to supply sufficient power gain. The second stage improves RF-to-DC signal ratio by class-AB type. Firstly, the biasing points of the two stages are selected in order to acquire the desired characteristics. Utilizing the software of load pull measurement, the output matching circuit could be determined by making trade-off between the output power level and the power-added-efficiency. Referred to the output optimal point of the drive stage and the input optimal point of the power stage, the best interface matching point is chosen to balance the mismatch. The input matching circuit is realized easily by conjugate match because it is assumed to influence the output power level slightly. The simulated result of output power is 19.4dBm and the PAE is 27.4% at the 1dB compression point. The maximum output power level is 20.5dBm at Pin=10dBm. The maximum value of PAE is 35.9% at the maximum output power point. The IIP3 point is about 20dBm and the OIP3 is 40dBm nearly. Nevertheless, the experimental outcome of maximum small-signal gain is 13.4dB at the central frequency of 32.4GHz. The maximum power-driving ability is 15dBm at Pin=12dBm. And the largest PAE value is 23%. This consequence is not similar completely with the simulated performances. The central frequency shifts from 38GHz to 32.4GHz. And the power-driving ability and gain
degrade compared with the original results. Discussed the reasons, the S-parameter of the WIN 0.15um power device at designed frequency and biasing voltage must be confirmed by test-key devices. And the parasitic capacitances of the RF pads have to deliberate whether it’s appropriate for the designed circuit or not. They are critical parameters to influence the performance crucially. The prospect of this categorical MMIC design is to extract carefully the transistors’ models. And any possible parasitic components are taken into account in order to obtain the efficient simulations. Therefore, the simulated sequence will relatively approach the experimental results.
The second part of this thesis describes a novel 2.4GHz bi-directional amplifier with gain control. This architecture includes two reflection-type amplifiers and a 90 degree branch-line hybrid. This approach can improve effectively the isolation and noise figure of the circuit to ameliorate the quality of output signal. This 90 degree branch-line circuit is realized on a FR4 board for these reasons and utilizes a new method to reduce the area to 7 square millimeters. So, this IC only includes these two imperative reflection-type amplifiers. The overall architecture of the reflection-type amplifier embraces a variable capacitance Ccont to control the gain and eliminate the influence of bonding wires, a parallel circuit of Cs and Ls to control the central frequency, the loaded impedance Rload and Lload in the drain end and a capacitance Cgs’ to modify the real part of the input impedance. The noise figure of this amplifier is between 4dB and 5dB approximately and the gain varies between 7.5dB and 16dB as the controlled voltage ranges from 2v to 0v. The specifications of this bi-directional amplifier are the same as them of the reflection-type amplifier described above. The future work must watch out the balance of the two reflection-type amplifiers and prevent the oscillation resulting from mismatch of the connection between the reflection-type amplifiers and the branch-line couple circuit.
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