Texas Instruments TCM4300 manual Modulation error percentage +100 s %

square-root raised-cosine (SQRC) shaping filter with a roll-off rate of α = 0.35 and converted to sampled analog form by two 9-bit digital-to-analog converters (DACs). The output of the DAC is then filtered by a continuous-time resistance-capacitance (RC) filter.

The TCM4300 generates a power amplifier (PA) control signal, PAEN, to enable the power supply for the PA. The start and stop times of the TDM burst are controlled by writing to a single bit, TXGO, in the DSP DStatCtrl register.

In the analog mode (MODE = 0), the DSP writes 8-bit I and Q samples into the TXI and TXQ data registers at a 40-ksps rate. These writes are timed by the SINT interrupt signal. The samples are fed to a low-pass filter before D/A conversion. In the transmit analog mode, PAEN is always set to 1.

The transmit section provides differential I and Q outputs (see Table 4-5) for both analog and digital modes. The differential dc offset for the TXI and TXQ outputs can be independently adjusted using the transmit offset registers.

Table 4±5. Transmit (TX) I and Q Channel Outputs

PARAMETER		MIN	TYP	MAX	UNIT
Peak output voltage full scale, centered at VCM	Differential		2.24		Vp
	Single ended		1.12
Nominal output-level (constellation radius) centered at	Differential		1.5		V
VCM	Single ended		0.75
Low-level drift			± 200		PPM/°C
Transmit error vector magnitude (EVM)			3%	4%
Resolution			8		bits
S/(N+D) ratio at differential outputs		48	52		dB
Gain error (I or Q channel)			± 8%	± 12%
Gain mismatch between I and Q				± 0.3	dB
Gain sampling mismatch between I and Q			20		ns
Zero code error differential				± 80	mV
Zero code error, each output, with respect to VCM				± 80	mV
Zero code error, I to Q, with respect to other channel (differential or				± 10	mV
single ended)
Load impedance, between P and N terminals		10			kΩ
Transmit offset DACs I and Q resolution			6		bits
Transmit offset DACs I and Q average step size		2.9	3.4	3.9	mV
Transmit offset DACs I and Q full-scale positive output			105.4		mV
Transmit offset DACs I and Q full-scale negative output			± 108.8		mV
Transmit offset DACs differential nonlinearity				± 1.1	LSB
Transmit offset DACs integral nonlinearity				± 1.1	LSB

Modulation Error: In the digital mode, during the transmit burst, the complex output of the transmitter circuits

consists of an ideal output s = I ideal + jQideal + error e = ei + jeq. In Table 4-5, the modulation error vector magnitude (EVM) is defined as the peak value of the magnitude of e relative to the ideal output:

e

Modulation error percentage +100 s %

Table 4±6 and Table 4±7 show the frequency response of the transmit section for digital and analog mode, respectively.

4±4