Chul-Dong Kim

Feedforward Amplifier using Equal Group-Delay Signal Canceller

In this paper, a new signal canceller that can matches an out-of-phase and a group delay of two path signals simultaneously is proposed. The simultaneous matching of the out-of-phase and the group delay time between two paths can makes a broadband signal cancellation possible. A feedforward linearizing power amplifier that adopts the proposed signal cancellers is fabricated on IMT-2000 base-station transmitting band. The main signal cancellation (or the 1st) loop of the fabricated feedforward amplifier cancel input signal more than 26.3dB and the intermodulation distortion (IMD) signal cancellation (or the 2nd) loop cancel IMD signal more than 15.2dB for 200MHz bandwidth. With the two-tone signals amplification process, the C/I ratio of the amplifier is improved 20.8dB, where the two tones are 2115MHz and 2165MHz, respectively

Doherty Amplifier Using Load Modulation and Phase Compensation DGS Microstrip Line

In this paper, a new Doherty power amplifier having the ideal harmonic termination condition that has been usually ignored is proposed. A defected ground structure (DGS) is adopted on the ground pattern of the output lambda/4 impedance inverter of the carrier amplifier and output offset transmission line of the peaking amplifier that are essential for proper load modulation operation of a conventional Doherty amplifier. As a result of the second and third harmonic termination, excellent improvement in power added efficiency (PAE), gain, maximum output power as well as linearity is obtained. The acquired improvements in gain, maximum output power (P1dB), PAE and adjacent channel leakage ratio (ACLR) to WCDMA 2FA signal are 0.42dB, 0.33dB, 12.7%, and 5.1dB, respectively. Moreover, physical length of microstrip line is shortened fairly by DGS, therefore the whole amplifier circuit size is considerably reduced

Dual-band predistortion power amplifier for digital cellular and IMT-2000 base-station application

This paper proposes a dual-band predistortion power amplifier using diplexer for digital cellular (f/sub 0/=880MHz) and IMT-2000(f/sub 0/=2140MHz) base station. Each high power amplifier is linearized by using predistortion method. The implemented predistorter uses reflection type IM generator with 3dB hybrid coupler for good reflection characteristic. The diplexer is composed of low pass filter using defected ground structure(DGS) microstrip line and high pass filter using high-Q lumped capacitors and distributed elements. For a forward link one-carrier CDMA IS-95 and WCDMA signal, the proposed dual-band predistortion power amplifier shows ACPR improvement of about 10dBc and 9.36dBc for cellular and IMT-2000 band of operation, respectively.

A Design of Predistortive High Power Amplifier using Carrier Complex Power Series Analysis

In this paper, a new carrier complex power series for linearizing the distortion effects of a HPA (High Power Amplifier) is proposed. Amplitude (AM-to-AM) and phase(AM-to-PM) nonlinear characteristics of HPA are combined to generate carrier complex power series. Inverse carrier complex power series of predistortor is also proposed. The fabricated HPA of IMT- 2000 band with a measured gain and P1dB are 34.06dB and 35.4dBm. With proposed series, C/I (Carrier to Intermodulation) ratio of HPA is improved by 17.01dB(@Pout = 25.43dBm/tone) with 2-tone at 2.1375GHz and 2.1425GHz.

A Novel Design of Frequency Multiplier Using Feedforward Technique and Defected Ground Structure

A novel design of frequency multiplier using a feedforward technique and a defected ground structure (DGS) is proposed. The feedforward loop in the proposed frequency multiplier suppresses the fundamental component (f₀) the dumb-bell or spiral shaped DGS diminish unwanted harmonics such as second, third, fourth. Due to the combination of the feedforward structure and the DGS, only the multiplied frequency component (2f₀, 3f₀, 4f₀) appears at the output port and the other unwanted components are suppressed excellently. The frequency multipliers are designed at 1 GHz of f₀, by the proposed technique and measured. The measured output power of2f₀, 3f₀, 4f₀ is -2.59 dBm, -5.36 dBm, -4.57 dBm, respectively, when the input power is 0 dBm

Group delay adjuster using resonance circuit with varactor diode

This paper presents a method to control group delay using resonance circuit. The group delay adjuster (GDA) which can control signal group delay time comprises a variable capacitance and a variable virtual inductor. These are coupled in parallel at a node and also controlled by two bias voltages respectively. A variable virtual inductor has realized a transmission line terminated a variable capacitor. When the proposed GDA is fabricated on cellular base-station transmitting band (869-894MHz), a group delay variation range of the fabricated GDA is about 1ns.

A design of predistortion linearizer using 2/sup nd/ order low frequency intermodulation signal injection

This paper presents a new predistortion methods which injects the 2nd order low frequency intermodulation signal of RF signal into the input bias line of the amplifier. We show this technique can suppress the 3rd IM and the 5th IM apparently by adjusting 2 factors, phase and amplitude, through mathematical analysis, and then confirm it with simulation. And we design digital cellular amplifier to show variation of the optimal performance without additional circuits or controls for the operating range. When the input signal CDMA IS-95 1FA was applied, measured ACPR improvements were 25dBc, 22.5dBc, and 6dBc at 0.855MHz, 1.25MHz, and 2.25MHz offset respectively. Also, when applying the CDMA IS-95 3FA, the measured ACPR improvement showed 16dBc at 0.885MHz offset.

Size Reduction of a Quasi Class-E High Power Amplifier Using Defected Ground Structure

In this work, a reduced size 20W quasi class-E Power Amplifier(PA) with defected ground structure load-network is presented for WCDMA base station application. Harmonic impedances required for the class E operation are satisfied by applying the dumbbell and the asymmetric spiral DGS. Open impedance for 2nd harmonic frequency which has the highest power and nearly short impedances for other higher order harmonics are provided by the proposed DGS load-network. The maximum Power Added Efficiency(PAE) of 70.2 % at the output power of 43.1 dBm with the saturated power gain of 12.7 dB is achieved by the proposed quasi class-E PA, which is comparable to the performance of the reference class-E PA. Total size of the proposed class-E PA is only and much smaller than the conventional class-E PA that is loaded with a number of open stubs.

Analog Controlled Adaptive Feedforward Amplifier for IMT-2000 Band

A novel adaptive design for feedforward amplifier linearizer with analog controller is proposed in this paper. Compared previous adaptive linearizing method, this is new design which does not require any pilot signal and intentional signal distortion. In main signal cancellation loop, magnitude and phase of two-path signal in subtracter are compared mutually and controlled for main signal cancellation. In distortion signal cancellation loop, gain and phase of each path is controlled to maintain constant, so that the same level and out-of phase of two-path distortion signal are obtained. A prototype feedforward amplifier with the proposed linearizer has been tested for 3-carrier IS-95 CDMA signals and 20.25dB ACPR is improved.

A Feedforward Power Amplifier with Loops that can reduce RX Band Noises Signals as well as Intermodulation Signals

In this paper, a new power amplifier is proposed for reduction of amplified RX band noise signals as well as TX band intermodulation distortion signals using feedforward technique. This proposed power amplifier, contains two loops-TX band intermodulation distortion signals cancellation loop and RX band noise signals cancellation loop, can provide duplexer with low TX path insertion loss for various wireless communication systems due to choice of loose RX attenuation characteristic. The proposed amplifier is implemented for IMT-2000 base station frequency band. Experimental results represent that the cancellation performance of intermodulation distortion signals and RX band noise signals are more than 31dB and 21dB, respectively.