A low out-of-band noise LTE transmitter with current-mode approach

Abstract

A 55nm CMOS current-mode transmitter for multistandard wireless communications (including LTE) that requires only 1.5mm 2 (with 4 output ports) is presented. The circuit is made up of two portions: a class A/B up-converter and a baseband that includes DAC, VGA, low-pass filter (two Biquad plus a passive first order) and class A/B signal conditioner. Combining a third order filter with the class A/B conditioner results in a reduction of both current consumption and RX-band noise injection. For LTE10, the consumption is 96mW and 34mW at 4dBm and at -10dBm output power, respectively. The complete transmitter gives -158dBc/Hz RX-band noise injection at 30MHz offset.

A low power/noise emission LTE fully class A/B transmitter with a programmable output balun

“…In fact a class B DAC requires less power, directly produces the required signal for the mixer and has a lower noise emission especially for signals with a high peak to average power ratio (PAPR) as in LTE. This avoids the need for a dedicated class A/B signal conditioner in front of the mixer thereby saving power, eliminating a significant noise contributor and reducing distortion compared to the solution proposed in [6]. The DAC is based on an n-type (sink only) topology that feeds directly the two virtual grounds of the pseudo-differential active first order filter.…”

“…Changing the value of R D the output power can be programmed in a very linear fashion. The closed loop architecture has therefore a much more linear V/I transfer function compared to a simple current mirror [6] where voltage compression and expansion occurs. As a consequence a very narrow passive filter can be used to strongly filter out the noise of the previous stages, without degrading linearity (the transfer function droop is .…”

“…6 compares current consumption (I and Q branches excluding the DAC) versus output power for the two transmitters. The old one [6] sees a constant impedance Z 1 at the primary while the new one (by changing the balun turn ratio at 0dBm) sees Z1/2 above 0dBm and 2Z1 below. Although at high power the new transmitter uses more current, below 0dBm (where consumption is crucial) the current saving is relevant.…”

“…In the first case, the most promising approach operates entirely in voltage-mode and is implemented with a passive up-converter driven by a filter and followed by pre-power amplifier (PPA) [1], [2]. In the second case, the standard solution is based on a current-mode power mixer, which has also the role of a prepower amplifier [3][4][5][6][7]. High power efficiency and low noise emission in the receive band (for FDD) mandate the use of class A/B solution, at least for the power stage.…”

“…The transmitter is an evolution of the one reported in [6], [7], conceptually shown in Fig. 1, whose operation is as follows.…”