| |
|
| |
| 介绍: |
Novel Approach Yields 100mW Bluetooth AmplifierAbstract: This article provides Bluetooth history from 1994 to present as well as Ericsson's role in the system evolution. Describes operation in the ISM band between 2400MHz and 2500MHz, using FHSS on 79 channels with 1MHz spacing. Article also describes using Bluetooth for long-range systems with 100mW output power. A discrete power amplifier (PA) is described including the bias and power control circuitry.
This integrated design meets its goals for performance and cost in support of class-1 long-range Bluetooth transmissions.
Bluetooth applications in the high-power 100m range require an amplifier capable of 100mW of output power at 2.4GHz. In contrast to traditional design techniques, a power amplifier (PA) developed by Maxim for long-range Bluetooth applications features integrated power control, comes in an ultra-small size at low cost, and requires a minimum number of external circuit elements. Background: About BluetoothEricsson Mobile Communications AB (Lund, Sweden) initiated a study in 1994 to investigate the feasibility of a low-power low-cost radio interface between mobile phones and their accessories.¹ The intent of the radio interface was to eliminate cables between mobile telephones and personal-computer (PC) cards and headsets. Initially, the link was called the multicommunicator (MC) link. As work on the new wireless link progressed, it became clear that there was no limit to the kinds of applications that could use a short-range radio link. An inexpensive short-range radio technology would make communications between portable devices economically feasible. However, for the system to succeed, a critical mass of industry support was necessary. In 1997, Ericsson approached other manufacturers of portable devices to raise interest in the technology, and, in 1998, a special interest group (SIG) comprised of companies from the mobile telephone and computer industry (Ericsson, Nokia, Intel, Toshiba, and IBM) was created. The consortium was formed to establish a de-facto standard for the air interface and the system software, and to promote the technology. In May 1998, the SIG publicly introduced the new wireless connectivity solution. The SIG dubbed the short-range wireless connectivity solution "Bluetooth" after the tenth-century king who united Denmark.
The Bluetooth system operates more or less in the unlicensed industrial-scientific-medical (ISM) band from 2400MHz to 2500MHz, with slight variations throughout the world. The system incorporates a frequency-hopping spread-spectrum (FHSS) scheme to share the spectrum among multiple users and to legally occupy the band if the radio-transmit power exceeds 0dBm (1mW). A total of 79 hop channels are used, with channel spacing of 1MHz and two-level frequency-shift-keying (FSK) modulation. The system achieves a bit rate of 1Mb/s and employs Gaussian modulation filtering with a bandwidth-time (BT) product (bandwidth per bits) of 0.5.
The system employs an air interface similar to that used in existing IEEE 802.11 FHSS wireless local-area-network (WLAN) systems, with some changes to enable use of low-cost hardware (for example, relaxed sensitivity, relaxed /static/ic5/dianlu/image rejection, and frequency hopping every packet with no fast turnaround time). However, the channel frequencies are the same and the modulation scheme is essentially the same as for two-level FSK. These modulation characteristics establish the type of amplifier required on the transmitter. A constant-envelope FSK modulation scheme is employed in Bluetooth, permitting the use of a saturated-mode transmit amplifier. Bluetooth for Long-Range ApplicationsThe Bluetooth system was originally conceived as a short-range link (up to 10m). However, as the possible Bluetooth applications expanded, potential end users expressed the desire for greater range. Given that the system receiver sensitivity is fixed at -70dBm, the practical solution to increasing range is to increase the radio transmit power. The need for greater transmit power leads to the definition of an additional class of radio-transmit output power. A peak transmit power of 100mW versus 1mW was chosen to ideally provide approximately a 10 x improvement in range to 100m and to keep the transmit power within the European ETSI regulation of 100mW effective isotropic radiant power (EIRP). The higher output created the need to add a separate PA after the RF transceiver (Figure 1). The higher transmit-power level became part of the Bluetooth radio-interface specification and is defined as class-1 operation.
Figure 1. Bluetooth radio system diagram.
The class-1 transmit-power specification is detailed in the radio section of the 1.0 version of the Bluetooth specification.² The output power is limited to a maximum transmit output power of 100mW. If class-1 power is used, the transmitter is required by the specification to implement power control to minimize overall interference and optimize the radio power consumption. The Bluetooth transmit specifications establish requirements for the overall radio. The PA specifications are derived from the system requirements and component characteristic of the elements that follow the PA (Figure 1). The RF switch, the RF bandpass filter, and the connector contribute a power loss of approximately 3dB (Figure 2).
Figure 2. The Bluetooth front end can be simplified to this representation.
Various specifications impact the transmit PA, including those covering spurious emissions and other operating conditions. All amplifier output specifications imply the use of modulated signals. In addition to the Bluetooth radio specifications, some specific system requirements arise from the implementation of a Bluetooth radio. The PA operating conditions include a supply voltage of +2.7VDC to +5VDC, a temperature range of -20°C to +60°C, input-power levels of 0dBm to +4dBm, supply current of less than 140mA, with target efficiency of 30 percent to 40 percent. The PA must provide an on-off control to permit power down during the receive timeslot. The PA should turn on/off in several microseconds. In the power-down mode, the PA collector current (ICC) should be less than 10µA. PA implementation objectives include a cost of less than $1.00, a size of less than 10mm x 10mm, and solution-design time of no more than one week.
Radio-transmit output-power specifications are implied over all operating conditions of supply voltage, temperature, and frequency. All power is measured in a 100kHz bandwidth. The minimum transmit output power is 0dBm, whereas the maximum transmit output power is +20dBm. The power can be controlled monotonically from +4dBm to +20dBm in minimum steps of 2dB and maximum steps of 8dB.
In-band spurious levels refer to the permissible levels of adjacent- and alternate-channel power, as well as any residual spurious signals within the 2400MHz to 2500MHz band. The primary regulatory limit is the -20dBc spectral power limit at the 1MHz band edge. All specifications are measured with an input signal that adheres to the Bluetooth modulating signal characteristics. All out-of-band spurious emissions refer to signals that are outside the 2400MHz to 2500MHz band. These specifications include maximum spurious levels of -36dBc from 30MHz to 1GHz, a maximum of -30dBc from 1GHz to 12.75GHz, and at least -47dBc from 1.8GHz to 1.9GHz and from 5.15GHz to 5.3GHz. Classical Approach The "classical" or traditional approach to designing a PA with power control centers around a two-stage PA constructed from discr |
| |
|
|
| |
|
|
|
|
|
芯片中文资料列表