In recent years, wireless terminals have gradually become the preferred solution for campus, airport, hospital and home access to the Internet by virtue of low cost, low power consumption and ease of networking. Wireless access technology has been rapidly developed and widely used. The design research of wireless transceiver modules has become an important research direction.
This paper introduces a 2.4 GHz ISM single-chip CMOS receiver RF front-end design for IEEE 802.11b/g wireless LAN standards. IEEE 802.11b is the mainstream product standard on the market, and IEEE 802.11g is one of the core standards of the IEEE 802.11 series. It is compatible with two other core standards, IEEE 802.11a and IEEE 802.11b, which support IEEE 802.11a OFDM ( Orthogonal Frequency Division Multiplexing (OFDM) and IEEE 802.11b CCK (Complementary Code Keying) coded DSS (Direct Sequence Spread Spectrum) modulation. The receiver designed in this paper is applied to the DSS modulation method.
1 system structureConsidering low cost, low power consumption and high integration, this paper uses a direct downconversion receiver structure for the wide channel bandwidth characteristics of IEEE802.11b/g itself. With advances in circuit technology and processes, the problems inherent in direct conversion have been greatly improved. In particular, DC offset and 1/f flicker noise problems can now effectively reduce their effects.
Table 1 lists a summary of the RF front-end performance of recent designs.
Figure 1 shows the system architecture of the receiver, including low noise amplifier, I / Q down converter, de DC coupling circuit, baseband linear amplifier and channel selection filter.
The DSS standard consists of 11 subchannels with 2 MHz bandwidth and a total channel bandwidth of 22 MHz. If the frame error rate is 8 & TImes;102, to achieve a sensitivity of -80 dBm, then
kNF+RSNR=174 dBm-10log(22 MHz)-80 dBm=20.6 dBm
Where: KNF is the noise figure; RSNR is the signal to noise ratio.
For the required FER, assuming RSNR ≈ 10 dB, and considering the RF filter's approximately 2 dB loss, the receiver's requirement is less than 8.6 dB.
The standard also requires 40 dB of adjacent channel rejection at -74 dBm, and the receiver's input 1 dB compression point is at least -30 dBm.
2 circuit implementation2.1 low noise amplifier
Figure 2 shows the specific implementation of the low noise amplifier circuit. The circuit uses a typical differential Cascode structure to increase on-chip interference rejection, reduce source parasitic inductance, and increase CMRR (common mode rejection ratio). However, the differential structure introduces more power than a single-ended input single-ended output.
In the following, only the left half of the symmetrical amplifier is analyzed. It is a narrowband Cascode low noise amplifier. This structure can achieve better noise performance. Ls and Ld use on-chip inductors, and Lc and Lg are implemented by bonded inductors. M1 and M3 are transconductance transistors. M2 and M4 connected by common gate improve the isolation between the output inputs and reduce the Miller effect of the drain capacitance Cgd of M1 and M3. Capacitors Cd, Cout, and Ld regulate the output matching and function to isolate the secondary circuit.
Of course, in addition to this, the influence of the capacitance Cs should also be considered when optimizing the circuit, but the equations (1) and (2) give the trend of the influence of each component on the circuit performance, which has guidance in designing the circuit. significance.
Carefully select the device parameters to get a noise figure of 0.84 dB. It can be seen from the simulation results in Figure 3 that the circuit optimization results make kNF very close to kNFmin.
Replacing the traditional tail current source with the inductor Le increases the common mode rejection ratio of the differential circuit, which saves DC voltage margin.
The following formula gives the reference formula for CMRR (denoted as RCMRR):
Where: ZA is the impedance of the differential pair tube to the ground.
The inductor uses a bonded inductor because it has the advantage of high Q and chip area savings.
Carefully balance between power and performance, achieving a low noise cancellation noise figure of 0.84 dB, a gain of 16 dB, S11 "-15 dB, and a current of 7.6 mA at 1.8 V DC.
2.2 I/Q down converter
Figure 4 shows a mixer for an I/Q quadrature downconverter. The design of the mixer requires careful selection of each parameter to balance the contradiction between gain, linearity and noise. Due to the strongest RF signal at the receiver, the mixer often has high linearity requirements. In this paper, the Gilbert cell active double-balanced mixer is used, which has a high isolation between each port. The source of the transconductance transistor is directly grounded to increase the linearity of the mixer. Current injection technology is also used in the circuit to reduce the low frequency noise of the mixer switching tube, while increasing the transconductance current and improving the linearity.
The IIP3 of the Gilbert unit can be expressed as:
Where: I and K are the bias current and transconductance parameters of the transconductance circuit, respectively.
When the local oscillator signal is a sine wave, the noise associated with the switch is:
Where: A is the amplitude of the local oscillator signal; ISW is the bias current of the switch to the tube.
To analyze equations (4) and (5), it is necessary to increase the bias current of the transconductance differential pair to improve the linearity of the mixer, and at the same time, it must reduce the bias current of the switch to the tube to reduce the switching noise. Current injection technology is needed to resolve the contradiction between the two.
The Hyde Mag vape is one of the newest innovations by renowned vape manufacturer, Hyde disposables. It provides the same quality flavors as it`s Hyde disposable predecessors, but has a quite unique design. The ergonomic form factor of the Hyde mag Disposable Vape is similar to that of the popular SMOK Mag vape mod.
Hyde Mag Vape Pod,Hyde Recharge 4500 Puff,China Hyde Mag Disposable Vape
Nanning Goodman Technology Co.,Ltd , https://www.goodmentech.com