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PGA970: Generated frequency is half of the expected frequency

Ric Otton
Prodigy 10 points
Part Number: PGA970

I am using the PGA970EVM and am facing issues with the waveform generator and bandpass filter. The generated frequency is half of what is set in the waveform generation settings (WFM).

In the below example I have configured the WFM Frequency to 1kHz (sine wave). When measured at pins TP27 and TP29, i.e. S1P and S1N, the frequency appears to be 500Hz. 

The PGA970 firmware is configured via the GUI with the following settings:

From the bandpass filter settings, the bandpass filter is able to let through the signal with the center frequency set at 1000Hz (250Hz Band Width) - even through the wave is measured at 500Hz, and according to the results on ADC1, amplitude is demodulated correctly (note that I have tied the output of the generated wave directly to J3 (ADC1) for testing).

I have also replicated this with a function generator, generating a 1kHz sine wave. When the bandpass filter is configured with a center frequency of 1000Hz, I am unable to get the demodulated amplitude but when configured with a center frequency of 2000Hz, the amplitude can be measured.

Why could this be happening?

  • 0
    TI__Mastermind 18900 points

    Hi Ric,

    Can you try 2 things for me?

    1. Read the waveform RAM from the waveform ram page and see if they match the table on the ADC settings page
    2. Change the amplitude to 295mV, repopulate the table and try again

    Thanks,

    -Cole

  • 0 in reply to Cole Macias
    Prodigy 10 points

    Hi Cole,

    The following information was collected by directly feeding a non-externally amplified waveform by altering the jumpers on J2 and J7 and skipping the ADC filtering by having J1 and J4 jumpers in place. I can find no correlation between the waveform data table on the ADC settings page and the Data and Waveform RAM page. Please refer to the following screenshots and files:

    300mV, 1kHz waveform configuation: (Please note the ADC1 Data reflects very close to 300mV)

    Data and waveform RAM programming table for the 300mV, 1kHz waveform configuration:

    300mV, 1kHz Waveform Data table file from the table under 'waveform generation' on the ADC settings page:

    Fullscreen 300mV PGA970 Waveform Data.txt Download 
    Address(Hex)	MSB(Hex)	LSB(Hex)
0	00	0C
2	00	25
4	00	3E
6	00	56
8	00	6F
A	00	88
C	00	A1
E	00	B9
10	00	D2
12	00	EB
14	01	03
16	01	1C
18	01	35
1A	01	4D
1C	01	66
1E	01	7E
20	01	97
22	01	AF
24	01	C8
26	01	E1
28	01	F9
2A	02	12
2C	02	2A
2E	02	42
30	02	5B
32	02	73
34	02	8C
36	02	A4
38	02	BC
3A	02	D5
3C	02	ED
3E	03	05
40	03	1D
42	03	36
44	03	4E
46	03	66
48	03	7E
4A	03	96
4C	03	AE
4E	03	C6
50	03	DE
52	03	F6
54	04	0E
56	04	25
58	04	3D
5A	04	55
5C	04	6D
5E	04	84
60	04	9C
62	04	B3
64	04	CB
66	04	E2
68	04	FA
6A	05	11
6C	05	28
6E	05	40
70	05	57
72	05	6E
74	05	85
76	05	9C
78	05	B3
7A	05	CA
7C	05	E1
7E	05	F8
80	06	0E
82	06	25
84	06	3C
86	06	52
88	06	69
8A	06	7F
8C	06	95
8E	06	AC
90	06	C2
92	06	D8
94	06	EE
96	07	04
98	07	1A
9A	07	30
9C	07	46
9E	07	5B
A0	07	71
A2	07	87
A4	07	9C
A6	07	B2
A8	07	C7
AA	07	DC
AC	07	F1
AE	08	07
B0	08	1C
B2	08	31
B4	08	45
B6	08	5A
B8	08	6F
BA	08	83
BC	08	98
BE	08	AC
C0	08	C1
C2	08	D5
C4	08	E9
C6	08	FD
C8	09	11
CA	09	25
CC	09	39
CE	09	4D
D0	09	60
D2	09	74
D4	09	87
D6	09	9B
D8	09	AE
DA	09	C1
DC	09	D4
DE	09	E7
E0	09	FA
E2	0A	0C
E4	0A	1F
E6	0A	32
E8	0A	44
EA	0A	56
EC	0A	69
EE	0A	7B
F0	0A	8D
F2	0A	9F
F4	0A	B0
F6	0A	C2
F8	0A	D4
FA	0A	E5
FC	0A	F7
FE	0B	08
100	0B	19
102	0B	2A
104	0B	3B
106	0B	4C
108	0B	5C
10A	0B	6D
10C	0B	7D
10E	0B	8E
110	0B	9E
112	0B	AE
114	0B	BE
116	0B	CE
118	0B	DE
11A	0B	ED
11C	0B	FD
11E	0C	0C
120	0C	1B
122	0C	2B
124	0C	3A
126	0C	48
128	0C	57
12A	0C	66
12C	0C	74
12E	0C	83
130	0C	91
132	0C	9F
134	0C	AD
136	0C	BB
138	0C	C9
13A	0C	D7
13C	0C	E4
13E	0C	F1
140	0C	FF
142	0D	0C
144	0D	19
146	0D	26
148	0D	32
14A	0D	3F
14C	0D	4B
14E	0D	58
150	0D	64
152	0D	70
154	0D	7C
156	0D	87
158	0D	93
15A	0D	9F
15C	0D	AA
15E	0D	B5
160	0D	C0
162	0D	CB
164	0D	D6
166	0D	E1
168	0D	EB
16A	0D	F6
16C	0E	00
16E	0E	0A
170	0E	14
172	0E	1E
174	0E	27
176	0E	31
178	0E	3A
17A	0E	43
17C	0E	4D
17E	0E	56
180	0E	5E
182	0E	67
184	0E	6F
186	0E	78
188	0E	80
18A	0E	88
18C	0E	90
18E	0E	98
190	0E	A0
192	0E	A7
194	0E	AE
196	0E	B6
198	0E	BD
19A	0E	C3
19C	0E	CA
19E	0E	D1
1A0	0E	D7
1A2	0E	DE
1A4	0E	E4
1A6	0E	EA
1A8	0E	F0
1AA	0E	F5
1AC	0E	FB
1AE	0F	00
1B0	0F	05
1B2	0F	0A
1B4	0F	0F
1B6	0F	14
1B8	0F	19
1BA	0F	1D
1BC	0F	22
1BE	0F	26
1C0	0F	2A
1C2	0F	2E
1C4	0F	31
1C6	0F	35
1C8	0F	38
1CA	0F	3C
1CC	0F	3F
1CE	0F	42
1D0	0F	44
1D2	0F	47
1D4	0F	4A
1D6	0F	4C
1D8	0F	4E
1DA	0F	50
1DC	0F	52
1DE	0F	54
1E0	0F	55
1E2	0F	57
1E4	0F	58
1E6	0F	59
1E8	0F	5A
1EA	0F	5B
1EC	0F	5B
1EE	0F	5C
1F0	0F	5C
1F2	0F	5C

    295mV, 1kHz waveform configuation: (Please note the ADC1 Data reflects very close to 295mV)

    Data and waveform RAM programming table for the 295mV, 1kHz waveform configuration: (Nothing appears to have changed).

    Note: If I power off, then on again, this table looks completely different every time, even when reconfigured with identical settings:

    295mV, 1kHz Waveform Data table file from the table under 'waveform generation' on the ADC settings page:

    Fullscreen 295mV PGA970 Waveform Data.txt Download 
    Address(Hex)	MSB(Hex)	LSB(Hex)
0	00	0C
2	00	24
4	00	3D
6	00	55
8	00	6D
A	00	86
C	00	9E
E	00	B6
10	00	CE
12	00	E7
14	00	FF
16	01	17
18	01	2F
1A	01	48
1C	01	60
1E	01	78
20	01	90
22	01	A8
24	01	C0
26	01	D9
28	01	F1
2A	02	09
2C	02	21
2E	02	39
30	02	51
32	02	69
34	02	81
36	02	99
38	02	B1
3A	02	C9
3C	02	E0
3E	02	F8
40	03	10
42	03	28
44	03	40
46	03	57
48	03	6F
4A	03	87
4C	03	9E
4E	03	B6
50	03	CD
52	03	E5
54	03	FC
56	04	14
58	04	2B
5A	04	42
5C	04	5A
5E	04	71
60	04	88
62	04	9F
64	04	B6
66	04	CD
68	04	E4
6A	04	FB
6C	05	12
6E	05	29
70	05	40
72	05	57
74	05	6D
76	05	84
78	05	9B
7A	05	B1
7C	05	C8
7E	05	DE
80	05	F4
82	06	0B
84	06	21
86	06	37
88	06	4D
8A	06	63
8C	06	79
8E	06	8F
90	06	A5
92	06	BB
94	06	D1
96	06	E6
98	06	FC
9A	07	11
9C	07	27
9E	07	3C
A0	07	51
A2	07	67
A4	07	7C
A6	07	91
A8	07	A6
AA	07	BB
AC	07	D0
AE	07	E4
B0	07	F9
B2	08	0E
B4	08	22
B6	08	37
B8	08	4B
BA	08	5F
BC	08	73
BE	08	87
C0	08	9B
C2	08	AF
C4	08	C3
C6	08	D7
C8	08	EB
CA	08	FE
CC	09	12
CE	09	25
D0	09	38
D2	09	4B
D4	09	5F
D6	09	72
D8	09	84
DA	09	97
DC	09	AA
DE	09	BD
E0	09	CF
E2	09	E2
E4	09	F4
E6	0A	06
E8	0A	18
EA	0A	2A
EC	0A	3C
EE	0A	4E
F0	0A	60
F2	0A	71
F4	0A	83
F6	0A	94
F8	0A	A6
FA	0A	B7
FC	0A	C8
FE	0A	D9
100	0A	EA
102	0A	FA
104	0B	0B
106	0B	1B
108	0B	2C
10A	0B	3C
10C	0B	4C
10E	0B	5C
110	0B	6C
112	0B	7C
114	0B	8C
116	0B	9C
118	0B	AB
11A	0B	BA
11C	0B	CA
11E	0B	D9
120	0B	E8
122	0B	F7
124	0C	05
126	0C	14
128	0C	23
12A	0C	31
12C	0C	3F
12E	0C	4D
130	0C	5B
132	0C	69
134	0C	77
136	0C	85
138	0C	92
13A	0C	A0
13C	0C	AD
13E	0C	BA
140	0C	C7
142	0C	D4
144	0C	E1
146	0C	ED
148	0C	FA
14A	0D	06
14C	0D	13
14E	0D	1F
150	0D	2B
152	0D	36
154	0D	42
156	0D	4E
158	0D	59
15A	0D	64
15C	0D	70
15E	0D	7B
160	0D	86
162	0D	90
164	0D	9B
166	0D	A5
168	0D	B0
16A	0D	BA
16C	0D	C4
16E	0D	CE
170	0D	D8
172	0D	E1
174	0D	EB
176	0D	F4
178	0D	FE
17A	0E	07
17C	0E	10
17E	0E	18
180	0E	21
182	0E	2A
184	0E	32
186	0E	3A
188	0E	42
18A	0E	4A
18C	0E	52
18E	0E	5A
190	0E	61
192	0E	68
194	0E	70
196	0E	77
198	0E	7E
19A	0E	84
19C	0E	8B
19E	0E	92
1A0	0E	98
1A2	0E	9E
1A4	0E	A4
1A6	0E	AA
1A8	0E	B0
1AA	0E	B5
1AC	0E	BB
1AE	0E	C0
1B0	0E	C5
1B2	0E	CA
1B4	0E	CF
1B6	0E	D4
1B8	0E	D8
1BA	0E	DD
1BC	0E	E1
1BE	0E	E5
1C0	0E	E9
1C2	0E	ED
1C4	0E	F1
1C6	0E	F4
1C8	0E	F7
1CA	0E	FB
1CC	0E	FE
1CE	0F	01
1D0	0F	03
1D2	0F	06
1D4	0F	08
1D6	0F	0B
1D8	0F	0D
1DA	0F	0F
1DC	0F	11
1DE	0F	12
1E0	0F	14
1E2	0F	15
1E4	0F	16
1E6	0F	17
1E8	0F	18
1EA	0F	19
1EC	0F	1A
1EE	0F	1A
1F0	0F	1A
1F2	0F	1B

  • 0 in reply to Ric Otton
    TI__Mastermind 18900 points

    Hi Ric,

    Ric Otton said:
    I can find no correlation between the waveform data table on the ADC settings page and the Data and Waveform RAM page.

    I forgot to give an important step, sorry about that. Please change the page to 0x1 and then capture the screenshot. You can also right click the center table and choose the export the data and put it in a code format like you did with the waveform data.

    See the 0x01 page address for waveform ram below.

    Ric Otton said:
    295mV, 1kHz waveform configuation: (Please note the ADC1 Data reflects very close to 295mV)

    How what the output waveform though. Did the frequency still stay around 500Hz?

    Thanks,

    -Cole

  • 0 in reply to Cole Macias
    Prodigy 10 points

    Hi Cole,

    I have rerun these configurations for page 0x01. No differences on page 0x01 were noticed between 300mV and 295mV configurations. The waveform is still producing 500Hz frequency.

    Data and waveform RAM programming table for the 295mV, 1kHz waveform configuration, page 0x01:

    Fullscreen 295mV 1kHz waveform RAM page 1.txt Download 
    Page Address: 	1							
Page	Word0	Word1	Word2	Word3	Word4	Word5	Word6	Word7
0	F490	FD45	61A6	8AF4	17C5	21AF	8AAF	35EE
1	B2CE	ED1D	7A49	08AA	09FF	5A29	0B7E	E775
2	6695	76CE	FCF7	975E	6A48	F68D	0484	D52D
3	165C	8C3D	6F9A	8E47	1EF6	FB8B	6F93	C68F
4	355A	6BF9	BD5C	0577	9229	5817	2411	D658
5	6A6A	B668	5746	8540	3F05	9D59	6CB3	F8C5
6	0D9F	AFD4	FC5E	0077	9CAE	7DC4	46FF	F7C1
7	EF73	CE30	2F31	014B	FF54	366F	470B	29D8
8	90C6	FCF8	FA08	1CE5	D8EC	0B47	FCB5	4753
9	FA23	1134	2743	850A	5B72	8289	D71C	2180
A	F6CF	D69A	3745	D243	AFCF	4C6A	0BAC	0F11
B	7B3E	4A37	E577	B44E	7FA1	A308	0B81	183A
C	4A6D	C65A	44F0	5AAF	2E9D	2CE3	1F24	3229
D	7BC2	BCA3	65DF	137F	5308	10D3	ACB3	226A
E	2AFF	CEA7	6862	F7B6	3EE9	AD8D	C186	43EC
F	5F98	FD82	25AF	2C05	7828	5FCF	EA3F	624B

    Data and waveform RAM programming table for the 300mV, 1kHz waveform configuration, page 0x01:

    Fullscreen 300mV 1kHz waveform RAM page 1.txt Download 
    Page Address: 	1							
Page	Word0	Word1	Word2	Word3	Word4	Word5	Word6	Word7
0	F490	FD45	61A6	8AF4	17C5	21AF	8AAF	35EE
1	B2CE	ED1D	7A49	08AA	09FF	5A29	0B7E	E775
2	6695	76CE	FCF7	975E	6A48	F68D	0484	D52D
3	165C	8C3D	6F9A	8E47	1EF6	FB8B	6F93	C68F
4	355A	6BF9	BD5C	0577	9229	5817	2411	D658
5	6A6A	B668	5746	8540	3F05	9D59	6CB3	F8C5
6	0D9F	AFD4	FC5E	0077	9CAE	7DC4	46FF	F7C1
7	EF73	CE30	2F31	014B	FF54	366F	470B	29D8
8	90C6	FCF8	FA08	1CE5	D8EC	0B47	FCB5	4753
9	FA23	1134	2743	850A	5B72	8289	D71C	2180
A	F6CF	D69A	3745	D243	AFCF	4C6A	0BAC	0F11
B	7B3E	4A37	E577	B44E	7FA1	A308	0B81	183A
C	4A6D	C65A	44F0	5AAF	2E9D	2CE3	1F24	3229
D	7BC2	BCA3	65DF	137F	5308	10D3	ACB3	226A
E	2AFF	CEA7	6862	F7B6	3EE9	AD8D	C186	43EC
F	5F98	FD82	25AF	2C05	7828	5FCF	EA3F	624B

    Also, I have included data for 0x08 since it seems possible that the waveform RAM is stored there according to the memory map. However, I have noticed that the data on page 0x08 changes every time I regenerate the same waveform.

    Data and waveform RAM programming table for the 295mV, 1kHz waveform configuration, page 0x08:

    Fullscreen 295mV 1kHz waveform RAM page 8.txt Download 
    Page Address: 	8							
Page	Word0	Word1	Word2	Word3	Word4	Word5	Word6	Word7
0	8804	4204	6C0B	010F	700D	9107	CE00	2509
1	E002	DE05	770C	1B0F	920C	DE05	E002	940A
2	C40D	0E08	3D00	8708	FE0D	D40E	C80A	2803
3	7906	0902	CF09	9E0E	520E	4B09	FF00	9107
4	C805	9902	600A	C00E	210E	D708	6D00	0E08
5	8B0E	5A0E	3809	4801	5107	7B0D	080F	BA0B
6	8804	BA0B	080F	4E0D	FC06	7801	5F09	680E
7	B00D	F40E	2C0B	B603	E404	140C	140F	060D
8	D007	BA0D	F10E	1B0B	9E03	2905	3F0C	190F
9	7E0E	680E	5F09	7801	FC06	360D	0D0F	F70B
A	0B0B	5703	4005	4D0C	1A0F	BA0C	F405	F802
B	7E0E	9709	2F01	6707	860D	FB0E	2C0B	B603
C	7C07	7B0D	FE0E	9C0B	2B04	7104	AB0B	0B0F
D	8C0B	060F	590D	6707	2F01	4B09	520E	AA0E
E	F10E	5C0B	CD03	2905	3F0C	190F	C70C	3706
F	420E	9E0E	F409	0902	A506	360D	0D0F	D90B

    Data and waveform RAM programming table for the 300mV, 1kHz waveform configuration, page 0x08:

    Fullscreen 300mV 1kHz waveform RAM page 8.txt Download 
    Page Address: 	8							
Page	Word0	Word1	Word2	Word3	Word4	Word5	Word6	Word7
0	F107	0A0E	2A0F	2A0B	4E03	9C05	910C	5C0F
1	3F0F	9F0D	1A07	AF01	FA09	DE0E	800E	4D09
2	690A	A402	3C06	260D	580F	480C	FA04	2504
3	F70A	1D0F	000E	0708	A100	2509	6F0E	DE0E
4	5B02	9F0A	050F	310E	4508	8800	1109	880E
5	0E06	0503	D40A	1D0F	000E	0708	D200	4D09
6	690A	4202	EE06	870D	440F	AE0B	DE03	1105
7	AA0D	3C0F	5C0B	C603	5705	9F0C	5C0F	D70C
8	D409	D10E	800E	2509	6F00	5A08	270E	0A0F
9	E105	0C0D	580F	2B0C	6D04	B304	3A0C	5B0F
A	440F	AE0B	DE03	4005	740C	5C0F	C90C	F805
B	1D03	2A0B	2A0F	E10D	9C07	4D01	AE09	B60E
C	380F	9F0D	4607	AF01	FA09	DE0E	6F0E	FD08
D	580F	0C0D	E105	3603	3B0B	2E0F	D60D	8707
E	F70A	D502	0E06	0C0D	580F	480C	CB04	8404
F	F901	0407	930D	420F	5C0B	9603	B305	BB0C

  • 0 in reply to Ric Otton
    TI__Mastermind 18900 points

    Hi Ric,

    Thanks for taking the data. Not the result I was expecting.

    Please give me a couple of days and let me see if I can reproduce you results.

    Best,

    -Cole